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Nucleic Acids Research Advance Access published online on November 11, 2009
Nucleic Acids Research, doi:10.1093/nar/gkp977
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© The Author(s) 2009. Published by Oxford University Press.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Gene Regulation, Chromatin and Epigenetics

A capping-independent function of MePCE in stabilizing 7SK snRNA and facilitating the assembly of 7SK snRNP

Yuhua Xue1,2, Zhiyuan Yang1, Ruichuan Chen2 and Qiang Zhou1,*

1Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA and 2Key Laboratory of the Ministry of Education for Cell Biology and Tumor Cell Engineering, School of Life Sciences, Xiamen University, Xiamen 361005, Fujian, China

*To whom correspondence should be addressed. Tel: +1 510 643 1697; Fax: +1 510 643 6334; Email: qzhou{at}berkeley.edu

Received July 17, 2009. Revised September 17, 2009. Accepted October 14, 2009.

The 7SK snRNP represents a major reservoir of activity where P-TEFb, a general transcription factor key for RNA polymerase II elongation, can be withdrawn to promote gene expression, cell growth and development. Within this complex, 7SK snRNA is a central scaffold that coordinates key protein–protein interactions and maintains P-TEFb in an inactive state. Although the stability of 7SK directly affects the amount of active P-TEFb in vivo, relatively little is known about how it is maintained and how the 7SK methylphosphate capping enzyme MePCE and LARP7, a La-related protein associated with the 3'-poly(U) of 7SK, contribute to this process. Here, we show that 7SK is capped by the LARP7-free MePCE and in probably a co-transcriptional manner prior to its sequestration into 7SK snRNP. However, upon interacting with LARP7 within 7SK snRNP, MePCE loses its capping activity, probably due to the occlusion of its catalytic center by LARP7. Despite its lack of capping activity in 7SK snRNP, MePCE displays a capping-independent function to promote the LARP7–7SK interaction, which in turn stabilizes 7SK and facilitates the assembly of a stable MePCE–LARP7–7SK subcomplex. Our data indicate that MePCE and LARP7 act cooperatively to stabilize 7SK and maintain the integrity of 7SK snRNP.

The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors.


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