Function of the mammalian La protein: evidence for its action in transcription termination by RNA polymerase III.

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Abstract
We have tested the hypothesis that the mammalian La protein, which appears to be required for accurate and efficient RNA polymerase III transcription, is a transcription termination factor. Our data suggest that 3′ foreshortened transcripts generated in La's absence are components of a novel transcription intermediate containing a paused polymerase. These transcripts are produced by fractionated transcription complexes, are synthesized with kinetics different from full-length transcripts, and are chasable to completion from the stalled transcription complexes. Together, these findings argue that termination by RNA polymerase III requires auxilliary factor(s) and implicate La as such a factor. Since La appears to facilitate transcript completion and release and also binds the resulting RNA product, it may be a regulator of RNA polymerase III transcription.