3'-PROCESSING AND TERMINATION OF MOUSE HISTONE TRANSCRIPTS SYNTHESIZED IN-VITRO BY RNA-POLYMERASE-II

The highly expressed mouse histone H2a-614 gene is located 800 nt 5' o f the histone H3-614 gene, There is a 140 nt sequence Iocated 500 nt f rom the end of the H2-614 mRNA which has been defined as a transcripti on termination site for RNA polymerase II, We established an in vitro transcription system in which both 3' end processing and transcription termination occur, A template containing the adenovirus major late pr omoter, a portion of the histone H2a-614 coding region, its 3' process ing signal, followed by the transcription termination site was transcr ibed in a nuclear extract prepared from mouse myeloma cells. Some of t he transcripts synthesized in the extract were cleaved at the histone processing site in a reaction which was dependent both on the hairpin binding factor and the U7 snRNP, The efficiency of histone 3' end form ation was similar both on synthetic transcripts and transcripts synthe sized by RNA polymerase II. Defined transcripts, which were not proces sed and which mapped to the transcription termination site, were relea sed from the template, suggesting that they were formed by transcripti on termination, Termination in vitro was dependent on a functional his tone processing signal.