UCSF

We have isolated and sequenced genes from Saccharomyces cerevisiae (SRP54SC) and Schizosaccharomyces pombe (SRP54sp) encoding proteins homologous to both the 54-kD protein subunit (SRP54mam) of the mammalian signal recognition particle (SRP) and the product of a gene of unknown function in Escherichia coli, ffh (Römisch, K., J. Webb, J. Herz, S. Prehn, R. Frank, M. Vingron, and B. Dobberstein. 1989. Nature (Lond.). 340:478-482; Bernstein H. D., M. A. Poritz, K. Strub, P. J. Hoben, S. Brenner, P. Walter. 1989. Nature (Lond.). 340:482-486). To accomplish this we took advantage of short stretches of conserved sequence between ffh and SRP54mam and used the polymerase chain reaction (PCR) to amplify fragments of the homologous yeast genes. The DNA sequences predict proteins for SRP54sc and SRP54sp that are 47% and 52% identical to SRP54mam, respectively. Like SRP54mam and ffh, both predicted yeast proteins contain a GTP binding consensus sequence in their NH2-terminal half (G-domain), and methionine-rich sequences in their COOH-terminal half (M-domain). In contrast to SRP54mam and ffh the yeast proteins contain additional Met-rich sequences inserted at the COOH-terminal portion of the M-domain. SRP54sp contains a 480-nucleotide intron located 78 nucleotides from the 5' end of the open reading frame. Although the function of the yeast homologues is unknown, gene disruption experiments in S. cerevisiae show that the gene is essential for growth. The identification of SRP54sc and SRP54sp provides the first evidence for SRP related proteins in yeast.