Human RagA and RagB is reported to be 52% identical to a putative GTPase of Saccharomyces cerevisiae, Gtr1p. According to the reported nucleotide sequence, we amplified human RagA and RagBs cDNAs from the human B cell cDNA library with PCR. Both cDNAs rescued a cold sensitivity of S. cerevisiae, gtr1-11. Furthermore, we introduced into the cloned human RagA cDNA, the mutation ‘T21L’ corresponding to the gtr1-11 mutation which has been reported to suppress not only all of rcc1-, temperature-sensitive mutants of Ran/Gsp1p GTPase GDP/GTP-exchanging factor, but also rna1-1, a temperature-sensitive mutant of Ran/Gsp1p GTPase-activating protein. The resulting RagAgtr1-11 cDNA partially, but significantly, suppressed both rcc1- and rna1-1 mutations. These results indicated that RagA and RagBs are functional homologues of S. cervisiae Gtr1p. Interestingly, while wild-type human RagA and RagBs were localized within the cytoplasm, similar to S. cerevisiae Gtr1p, the mutated human RagAgtr1-11 corresponding to a dominant negative form of RagA was distributed in discrete speckles in the nucleus, being localized side by side with SC-35, a non-snRNP of the splicing complex. In contrast, a dominant positive form of RagA, Q66L was localized in the cytoplasm. Thus, RagA was suggested to shuttle between the cytoplasm and the nucleus, depending on the bound nucleotide state.
RagA is a functional homologue of S. cerevisiae Gtr1p involved in the Ran/Gsp1-GTPase pathway
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E. Hirose, N. Nakashima, T. Sekiguchi, T. Nishimoto; RagA is a functional homologue of S. cerevisiae Gtr1p involved in the Ran/Gsp1-GTPase pathway. J Cell Sci 1 January 1998; 111 (1): 11–21. doi: https://doi.org/10.1242/jcs.111.1.11
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