Recently, a number of novel small cytoplasmic ribonucleoprotein particles have been identified that comprise RNA and protein subunits related to the signal recognition particle (SRP). Here we discuss the latest results on the structure and functions of SRP together with the structures and putative functions of the novel SRP-related ribonucleoprotein particles.

REFERENCES

Adeniyi-Jones
S.
,
Zasloff
M.
(
1985
).
Transcription, processing and nuclear transport of a B1 Alu RNA species complementary to an intron of the murine-fetoprotein gene.
Nature
317
,
81
84
Andreazzoli
M.
,
Gerbi
S. A.
(
1991
).
Changes in 7SL RNA conformation during the signal recognition particle cycle.
EMBO J
10
,
767
777
Bacher
G.
,
Lutcke
H.
,
Jungnickel
B.
,
Rapoport
T. A.
,
Dobberstein
B.
(
1996
).
Regulation by the ribosome of the GTPase of the signal recognition particle during protein targeting.
Nature
381
,
248
251
Batzer
M. A.
,
Arcot
S.S.P.
,
Alegria-Hartman
J.W.
,
Kass
M.
,
Milligan
D.H.
,
Kimpton
S.M.
,
Gill
C.
,
Hochmeister
P.
,
Ioannou
M.
,
Herrera
P.A.
, et al. 
(
1996
).
Genetic variation of recent Alu insertions in human populations.
J. Mol. Evol
42
,
22
29
Belin
D.
,
Bost
S.
,
Vassalli
J.-D.
,
Strub
K.
(
1996
).
A two-step recognition of signal sequences determines the translocation efficiency of proteins.
EMBO J
15
,
468
478
Bernstein
H. D.
,
Poritz
M. A.
,
Strub
K.
,
Hoben
P. J.
,
Brenner
S.
,
Walter
P.
(
1989
).
Model for signal sequence recognition from amino-acid sequence of 54k subunit of signal recognition particle.
Nature
340
,
482
486
Bourne
H. R.
,
Sanders
D. A.
,
McCormick
F.
(
1991
).
The GTPase superfamily: conserved structure and molecular mechanism.
Nature
349
,
117
127
Bovia
F.
,
Bui
N.
,
Strub
K.
(
1994
).
The heterodimeric subunit SRP9/14of the signal recognition particle functions as permuted single polypeptide chain.
Nucl. Acids Res
22
,
2028
2035
Bovia
F.
,
Fornallaz
M.
,
Leffers
H.
,
Strub
K.
(
1995
).
The SRP9/14 subunit of the signal recognition particle (SRP) is present in more than 20-fold excess over SRP in primate cells and exists primarily free but also in complex with small cytoplasmic Alu RNAs.
Mol. Biol. Cell
6
,
471
484
Brown
J. D.
,
Hann
B. C.
,
Medzihradszky
K. F.
,
Niwa
M.
,
Burlingame
A. L.
,
Walter
P.
(
1994
).
Subunits of the Saccharomyces cerevisiae signal recognition particle required for its functional expression.
EMBO J
13
,
4390
4400
Brown
S.
(
1989
).
Time of action of 4.5 S RNA in Escherichia coli translation.
J. Mol. Biol
209
,
79
90
Chang
D. Y.
,
Maraia
R. J.
(
1993
).
A cellular protein binds B1 and Alu small cytoplasmic RNAs in vitro.
J. Biol. Chem
268
,
6423
6428
Chang
D.-Y.
,
Nelson
B.
,
Bilyeu
T.
,
Hsu
K.
,
Darlington
G.
,
Maraia
R. J.
(
1994
).
A human Alu RNA-binding protein whose expression is associated with accummulation of small cytoplasmic Alu RNA.
Mol. Cell. Biol
14
,
3949
3959
Chang
D. Y.
,
Sasaki Tozawa
N.
,
Green
L. K.
,
Maraia
R. J.
(
1995
).
A trinucleotide repeat-associated increase in the level of Alu RNA-binding protein occurred during the same period as the major Alu amplification that accompanied anthropoid evolution.
Mol. Cell Biol
15
,
2109
2116
Connolly
T.
,
Rapiejko
P. J.
,
Gilmore
R.
(
1991
).
Requirement of GTP hydrolysis for dissociation of the signal recognition particle from its receptor.
Science
252
,
1171
1173
Garcia
P. D.
,
Walter
P.
(
1988
).
Full-length prepro-alpha-factor can be translocated across the mammalian microsomal membrane only if translation has not terminated.
J. Cell Biol
106
,
1043
1048
Hauser
S.
,
Bacher
G.
,
Dobberstein
B.
,
Lutcke
H.
(
1995
).
A complex of the signal sequence binding protein and the SRP RNA promotes translocation of nascent proteins.
EMBO J
14
,
5485
5493
Jelinek
W. R.
,
Leinwand
L.
(
1978
).
Low molecular weight RNAs hydrogen-bonded to nuclear and cytoplasmic poly(A)-terminated RNA from cultured chinese hamster ovary cells.
Cell
15
,
205
214
Jelinek
W. R.
,
Schmid
C. W.
(
1982
).
Repetitive sequences in eukaryotic DNA and their expression.
Annu. Rev. Biochem
51
,
813
844
Jungnickel
B.
,
Rapoport
T. A.
(
1995
).
A posttargeting signal sequence recognition event in the endoplasmic reticulum membrane (see comments).
Cell
82
,
261
270
Kapitonov
V.
,
Jurka
J.
(
1996
).
The age of Alu subfamilies.
J. Mol. Evol
42
,
59
65
Kariya
Y.
,
Kato
K.
,
Hayashizaki
Y.
,
Himeno
S.
,
Tarui
S.
,
Matsubara
K.
(
1987
).
Revision of consensus sequence of human Alu repeats- a review.
Gene
53
,
1
10
Kobayashi
S.
,
Goto
S.
,
Anzai
K.
(
1991
).
Brain-specific small RNA transcript of the identifier sequences is present as a 10 S ribonucleoprotein particle.
J. Biol. Chem
266
,
4726
4730
Labuda
D.
,
Zicetkiewicz
E.
(
1994
).
Evolution of secondary structure in the family of 7SL-like RNAs.
J. Mol. Evol
39
,
506
518
Larsen
N.
,
Zwieb
C.
(
1996
).
The signal recognition particle database (SRPDB).
Nucl. Acids Res
24
,
80
81
Lauffer
L.
,
Garcia
P. D.
,
Harkins
R. N.
,
Coussens
L.
,
Ullrich
A.
,
Walter
P.
(
1985
).
Topology of the SRP receptor in the endoplasmic reticulum membrane.
Nature
318
,
334
338
Lauring
B.
,
Sakai
H.
,
Kreibich
G.
,
Wiedmann
M.
(
1995
).
Nascent polypeptide-associated complex protein prevents mistargeting of nascent chains to the endoplasmic reticulum.
Proc. Nat. Acad. Sci. USA
92
,
5411
5415
Leinwand
L. A.
,
Wydro
R. M.
,
Nadal-ginard
B.
(
1982
).
Small RNA molecules related to the Alu family of repetitive DNA sequences.
Mol. Cell. Biol
2
,
1320
1330
Liao
X.
,
Selinger
D.
,
Althoff
S.
,
Chiang
A.
,
Hamilton
D.
,
Ma
M.
,
Wise
J. A.
(
1992
).
Random mutagenesis of Schizosaccharomyces pombe SRP RNA: lethal and conditional lesions cluster in presumptive protein binding sites.
Nucl. Acids Res
20
,
1607
1615
Liu
W. M.
,
Maraia
R. J.
,
Rubin
C. M.
,
Schmid
C. W.
(
1994
).
Alu transcripts: cytoplasmic localisation and regulation by DNA methylation.
Nucl. Acids Res
22
,
1087
1095
Liu
W. M.
,
Chu
W. M.
,
Choudary
P. V.
,
Schmid
C. W.
(
1995
).
Cell stress and translational inhibitors transiently increase the abundance of mammalian SINE transcripts.
Nucl. Acids Res
23
,
1758
1765
Lutcke
H.
(
1995
).
Signal recognition particle (SRP), a ubiquitous initiator of protein translocation.
Eur. J. Biochem
228
,
531
550
Maraia
R. J.
(
1991
).
The subset of mouse B1 (Alu-equivalent) sequencesexpressed as small processed cytoplasmic transcripts.
Nucl. Acids Res
19
,
5695
5702
Maraia
R. J.
,
Driscoll
C. T.
,
Bilyeu
T.
,
Hsu
K.
,
Darlington
G. J.
(
1993
).
Multiple dispersed loci produce small cytoplasmic Alu RNA.
Mol. Cell Biol
13
,
4233
4241
Martignetti
J. A.
,
Brosius
J.
(
1993
).
BC200 RNA: a neural RNA polymerase III product encoded by a monomeric Alu element.
Proc. Nat. Acad. Sci. USA
90
,
11563
11567
Martignetti
J. A.
,
Brosius
J.
(
1993
).
Neural BC1 RNA as an evolutionary marker: guinea pig remains a rodent.
Proc. Nat. Acad. Sci. USA
90
,
9698
9702
Miller
J. D.
,
Wilhelm
H.
,
Gierasch
L.
,
Gilmore
R.
,
Walter
P.
(
1993
).
GTP binding and hydrolysis by the signal recognition particle during initiation of protein translocation.
Nature
366
,
351
354
Miller
J. D.
,
Tajima
S.
,
Lauffer
L.
,
Walter
P.
(
1995
).
The beta subunit of the signal recognition particle receptor is a transmembrane GTPase that anchors the alpha subunit, a peripheral membrane GTPase, to the endoplasmic reticulum membrane.
J. Cell Biol
128
,
273
282
Ogg
S. C.
,
Walter
P.
(
1995
).
SRP samples nascent chains for the presence of signal sequences by interacting with ribosomes at a discrete step during translation elongation.
Cell
81
,
1075
1084
Powers
T.
,
Walter
P.
(
1995
).
Reciprocal stimulation of GTP hydrolysis by two directly interacting GTPases.
Science
269
,
1422
1424
Powers
T.
,
Walter
P.
(
1996
).
The nascent polypeptide-associated complex modulates interactions between the signal recognition particle and the ribosome.
Curr. Biol
6
,
331
338
Quentin
Y.
(
1992
).
Fusion of a free left Alu monomer and a free right Alu monomer at the origin of the Alu family in the primate genome.
Nucl. Acids Res
20
,
487
493
Quentin
Y.
(
1992
).
Origin of the Alu family: a family of Alu-like monomers gave birth to the left and right arms of the Alu elements.
Nucl. Acids Res
20
,
3397
3401
Quentin
Y.
(
1994
).
A master sequence related to a free left Alu monomer (FLAM) at the origin of the B1 family in rodent genomes.
Nucl. Acids Res
22
,
2222
2227
Rapiejko
P.
,
Gilmore
R.
(
1992
).
Protein translocation across the ER requires a functional GTP binding site in the-subunit of the signal recognition particle receptor.
J. Cell Biol
117
,
493
503
Rapoport
T. A.
,
Heinrich
R.
,
Walter
P.
,
Schulmeister
T.
(
1987
).
Mathematical modeling of the effects of the signal recognition particle on translation and translocation of proteins across the endoplasmic reticulum membrane.
J. Mol. Biol
195
,
621
636
Schatz
G.
,
Dobberstein
B.
(
1996
).
Common principles of protein translocation across membranes.
Science
271
,
1519
1526
Schoeniger
L. O.
,
Jelinek
W. R.
(
1986
).
4.5S RNA is encoded by hundreds of tandemly linked genes, has a short half-life, and is hydrogen bonded in vivo to poly(A)-terminated RNAs in the cytoplasm of cultured mouse cells.
Mol. Cell. Biol
6
,
1508
1519
Siegel
V.
,
Walter
P.
(
1986
).
Removal of the Alu structural domain from signal recognition particle leaves its protein translocation activity intact.
Nature
320
,
81
84
Siegel
V.
,
Walter
P.
(
1988
).
Each of the activities of signal recognition particle (SRP) is contained within a distinct domain: analysis of biochemical mutants of SRP.
Cell
52
,
39
49
Strub
K.
,
Walter
P.
(
1989
).
Isolation of a cDNA clone of the 14-kDa subunit of the signal recognition particle by cross-hybridization of differently primed polymerase chain reactions.
Proc. Nat. Acad. Sci. USA
86
,
9747
9751
Strub
K.
,
Walter
P.
(
1990
).
Assembly of the Alu domain of the signal recognition particle (SRP): dimerization of the two protein components is required for efficient binding of SRP RNA.
Mol. Cell. Biol
10
,
777
784
Strub
K.
,
Moss
J.
,
Walter
P.
(
1991
).
Binding sites of the 9-and 14-kilodalton heterodimeric protein subunit of the signal recognition particle (SRP) are contained exclusively in the Alu domain of SRP RNA and contain a sequence motif that is conserved in evolution.
Mol. Cell. Biol
11
,
3949
3959
Tiedge
H.
,
Chen
W.
,
Brosius
J.
(
1993
).
Primary structure, neural-specific expression, and dendritic location of human BC200 RNA.
J. Neurosci
13
,
2382
2390
van Venrooij
W. J.
,
Slobbe
R. L.
,
Pruijn
G. J.
(
1993
).
Structure and function of La and Ro RNPs.
Mol. Biol. Rep
18
,
113
119
Walter
P.
,
Ibrahimi
I.
,
Blobel
G.
(
1981
).
Translocation of proteins across the endoplasmic reticulum I. Signal recognition protein (SRP) binds to in vitro assembled polysomes synthesizing secretory protein.
J. Cell Biol
91
,
545
550
Walter
P.
,
Johnson
A. E.
(
1994
).
Signal sequence recognition and protein targeting to the endoplasmic reticulum membrane.
Annu. Rev. Cell Biol
10
,
87
119
Watson
J. B.
,
Sutcliffe
J. G.
(
1987
).
Primate brain specific cytoplasmic transcript of the Alu repeat family.
Mol. Cell. Biol
7
,
3324
3327
Weiner
A. M.
,
Deininger
P. L.
,
Efstratiadis
A.
(
1986
).
Nonviral retroposons: genes, pseudogenes, and transposable elements generated by the reverse flow of genetic information.
Annu. Rev. Biochem
55
,
631
661
Wiedmann
B.
,
Sakai
H.
,
Davis
T. A.
,
Wiedmann
M.
(
1994
).
A protein complex required for signal-sequence-specific sorting and translocation.
Nature
370
,
434
440
Wiedmann
M.
,
Kurzchalia
T. V.
,
Bielka
H.
,
Rapoport
T. A.
(
1987
).
Direct probing of the interaction between the signal sequence of nascent preprolactin and the signal recognition particle by specific cross-linking.
J. Cell Biol
104
,
201
208
Wolin
S. L.
(
1994
).
From the elephant to E. coli: SRP dependent protein targeting.
Cell
77
,
787
790
Zwieb
C.
(
1985
).
The secondary structure of the 7SL RNA in the signal recognition particle: functional implications.
Nucl. Acids Res
13
,
6105
6124
This content is only available via PDF.