Cloning of murine translation initiation factor 6 and functional analysis of the homologous sequence YPR016c in Saccharomyces cerevisiae

The cDNA sequence of a murine gene whose expression was up-regulated after epidermal injury was cloned utilizing differential display. The full-length cDNA was isolated by 3' and 5' rapid amplification of cDNA ends from mouse liver. The predicted protein is >97% identical to the human sequence for e ukaryotic translation initiation factor (eIF) 6, thus identifying the gene as murine eIF6, Functional studies of the yeast eIF6 homolog, YPR016c, were initiated in Saccharomyces cerevisiae to determine the cellular role(s) of eIF6. Complete deletion of the YPR016c coding sequence was lethal. Viabili ty was restored in the presence of either YPR016c of murine eIF6, when eith er was expressed as aminoterminal green fluorescent protein fusion protein. Moreover, both fusion proteins localized to nuclear/perinuclear compartmen ts in their respective yeast strains. When the expression of YPR016c-green fluorescent protein was repressed, there was a dramatic reduction in the 60 S ribosomal subunit and polysome content and decreased 80S monosome conten t. Additionally, the YPR016c-depleted cells arrested in G(1). These studies show that YPR016c, which encodes yeast eIF6, is necessary for maximal poly some formation and plays an important role in determining free 60 S ribosom al subunit content.