EVIDENCE FOR A PROTEIN DOMAIN SUPERFAMILY SHARED BY THE CYCLINS, TFIIB AND RB P107/

Cyclins, TFIIB and RB play major roles in cell cycle and/or gene regul ation. Earlier work has suggested common ancestry for the TFIIB repeat s and RB pocket B which share 20% sequence identity. We now report tha t database searches with profiles based on a multiple alignment of cyc lin core regions (the 'cyclin box') detect the TFIIB repeats with equi valent scores to divergent cyclins. Several features of the sequences support the notion of common ancestry: e.g. cyclins A/B, C and D share similar to 20 - 30% identity but each have similar to 15 - 20% identi ty with vertebrate TFIIB, showing that conserved cyclin features under lie the match. These results suggest the presence of a domain superfam ily, which we term the TR domain, in nuclear regulatory proteins belon ging to the TFIIB, cyclin and RB families, that has been duplicated ma ny times during eukaryotic evolution. The TR domain appears to functio n in protein - protein interactions.