| Abstrakt: |
Yeast and other fungi contain a soluble elongation factor 3 (EF‐3) which is required for growth and protein synthesis. EF‐3 contains two ABC cassettes, and binds and hydrolyses ATP. We identified a homolog of the YEF3gene in the Saccharomyces cerevisiaegenome database. This gene, designated YEF3B, is 84% identical in protein sequence to YEF3, which we will now refer to as YEF3A. YEF3Bis not expressed during growth under laboratory conditions, and thus cannot rescue growth of YEF3Adeletion strains. However, YEF3Bcan take the place of YEF3A in vivowhen expressed from the YEF3Aor ADH1promoters. The products of the YEF3Aand YEF3Bgenes, EF‐3A and EF‐3B, respectively, were expressed from the ADH1promoter and purified. Both factors possessed basal and ribosomal‐stimulated ATPase activity, and had similar affinity for yeast ribosomes (103 to 113 nm). Kmvalues for ATP were similar, but the Kcatvalues differed significantly. Ribosome‐dependent ATPase activity of EF‐3A was more efficient than EF‐3B, since the Kcatand Kcat/Kmvalues for EF‐3A were about two‐fold higher; however, the difference in Kcat/Kmvalues between the two factors was small for basal ATPase activity. © 1998 John Wiley & Sons, Ltd. |
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