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

Abstract

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a major reservoir of activity where P-TEFb, a general transcription factor key for RNA polymerase II elongation, can be withdrawn to promote gene expression, cell growth and development.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.

Cell cycle gene-specific control of transcription has a critical role in proliferation of primordial germ cells

“…The number of cells in G1 phase was significantly increased, while the number in G2/M phase was apparently decreased, by knockdown of Larp7 or MePCE; simultaneous knockdown of Larp7 and MePCE resulted in additive effects ( Fig. 2A; Xue et al 2009). These results are consistent with the finding that the cell cycle in Larp7-deficient PGCs in embryos is abnormal (Fig.…”

Neonatal expression of RNA-binding protein IGF2BP3 regulates the human fetal-adult megakaryocyte transition

“…Indeed, both of the 7SK-stabilizing factors underwent full downregulation during neonatal megakaryopoiesis ( Figure 2E and Supplemental Figure 3A). Numerous studies have documented tight coupling of 7SK snRNA levels with its stabilizing factors (26)(27)(28)(29)(30). However, the stabilizing factors' decline in neonatal megakaryocytes occurred in the absence of a proportionate drop in 7SK snRNA levels, which remained 2.5-fold higher than adult levels ( Figure 2F and Supplemental Figure 3B).…”

The association of a La module with the PABP-interacting motif PAM2 is a recurrent evolutionary process that led to the neofunctionalization of La-related proteins

“…5 Of the LARP families studied for function so far, LARP7 is the best known. Vertebrate LARP7 binds specifically to 7SK snRNA, in part via its 39UUU-OH, forming the core of a multicomponent ribonucleoprotein complex (the 7SK snRNP) involved in regulating Pol II transcription elongation by sequestering the positive elongation factor pTEF-b in an inactive state (Diribarne and Bensaude 2009;Bayfield et al 2010;Xue et al 2010). Also, Tetrahymena LARP7 (also named p65) binds to telomerase RNA and is essential for its accumulation in vivo (Witkin and Collins 2004;Singh et al 2012).…”