A broad but restricted requirement for TAF-5 (human TAFII100) for embryonic transcription in Caenorhabditis elegans.

As conserved components of the transcription factor (TF) IID- and TFTC/SAGA-related complexes, TATA-binding protein-associated factors (TAF(II)s) are important for eukaryotic mRNA transcription. In yeast, genetic analyses suggest that, although some individual TAF(II)s are required for transcription of most genes, others have highly specialized functions. Much less is known about the functions of TAF(II)s in metazoans, which have more complex genomes that include many tissue-specific genes. TAF-5 (human (h) TAF(II)100) is of particular interest because it is predicted to have an important structural role. Here we describe the first genetics-based analysis of TAF-5 in a metazoan. By performing RNA interference in Caenorhabditis elegans embryos, which can survive for several cell generations without transcription, we found that taf-5 is important for a significant fraction of transcription. However, TAF-5 is apparently not essential for the expression of multiple developmental and other metazoan-specific genes. This phenotype remarkably resembles the previously described effects of similarly depleting two C. elegans histone fold TAF(II)s, TAF-9 (hTAF(II)31/32) and TAF-10 (hTAF(II)30), but is distinct from the widespread transcription block caused by TAF-4 (hTAF(II)130) depletion. Our findings suggest that TAF-5, TAF-9, and TAF-10 are part of a functional module of TFIID- and TFTC/SAGA-related complexes that can be bypassed in many metazoan-specific genes.