MULTIFUNCTIONAL PROTEINS SUGGEST CONNECTIONS BETWEEN TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL PROCESSES

Recent findings indicate that substantial cross-talk may exist between transcriptional and post-transcriptional processes. Firstly, there ar e suggestions that specific promoters influence the post-transcription al fate of transcripts, pointing to communication between protein comp lexes assembled on DNA and nascent pre-mRNA. Secondly, an increasing n umber of proteins appear to be multifunctional, participating in trans criptional and post-transcriptional events. The classic example is TFI IIA, required for both the transcription of 5S rRNA genes and the pack aging of 5S rRNA. TFIIIA is now joined by the Y-box proteins, which bi nd DNA (transcription activation and repression) and RNA (mRNA packagi ng). Furthermore, the tumour suppressor WT1, at first thought to be a typical transcription factor, may also be involved in splicing; conver sely, hnRNP K, a bona fide pre-mRNA-binding protein, appears to be a t ranscription factor. Other examples of multifunctional proteins are me ntioned: notably PTB, Sxl, La and PU.1. It is now reasonable to assert that some proteins, which were first identified as transcription fact ors, could just as easily have been identified as splicing factors, hn RNP, mRNP proteins and vice versa. It is no longer appropriate to view gene expression as a series of compartmentalised processes; instead, multifunctional proteins are likely to co-ordinate different steps of gene expression.