CONSERVATION AND DIVERSITY IN THE STRUCTURE OF TRANSLATION INITIATION-FACTOR EIF3 FROM HUMANS AND YEAST

Initiation factor eIF3 plays a central role in the initiation pathway, influencing ribosome association, ternary complex binding to 40S subu nits, and mRNA binding, in part through an interaction with eIF4F. We are attempting to clone and sequence DNAs encoding the subunits of thi s complex factor. Mammalian eIF3 comprises 10 subunits; full-length hu man cDNAs have been cloned for eight of these, and partial clones are in hand for the remaining two. Yeast eIF3 comprises at least seven sub units, with six of the seven genes identified and sequenced. Compariso n of eIF3 subunit sequences between human and yeast reveals an unexpec tedly large diversity of structure. Surprisingly, comparisons with oth er sequences in the data base suggest that some of the eIF3 subunits m ay have functions apart from the eIF3 complex. Work is in progress to use the cloned DNAs as tools for elucidating the structure of eIF3 and its interactions with other initiation factors.