The yeast SIS1 protein, a DnaJ homolog, is required for the initiation of translation.
The S. cerevisiae SIS1 gene is essential and encodes a heat shock protein with similarity to the bacterial DnaJ protein. At the nonpermissive temperature, temperature-sensitive sis1 strains rapidly accumulate 80S ribosomes and have decreased amounts of polysomes. Certain alterations in 60S ribosomal subunits can suppress the temperature-sensitive phenotype of sis1 strains and prevent the accumulation of 80S ribosomes and the loss of polysomes normally seen under conditions of reduced SIS1 function. Analysis of sucrose gradients for SIS1 protein shows that a large fraction of SIS1 is associated with 40S ribosomal subunits and the smaller polysomes. These and other results indicate that SIS1 is required for the normal initiation of translation. Because DnaJ has been shown to mediate the dissociation of several protein complexes, the requirement of SIS1 in the initiation of translation might be for mediating the dissociation of a specific protein complex of the translation machinery.
Cold Spring Harbor Laboratory, New York 11724.
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D000595:Amino Acid Sequence; D001483:Base Sequence; D004252:DNA Mutational Analysis; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D050956:HSP40 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D012269:Ribosomal Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid
D005656:Fungal Proteins; D050956:HSP40 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D012269:Ribosomal Proteins; C070320:SIS1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins