LARP7 is a stable component of the 7SK snRNP while P-TEFb, HEXIM1 and hnRNP A1 are reversibly associated.
Regulation of the elongation phase of RNA polymerase II transcription by P-TEFb is a critical control point for gene expression. The activity of P-TEFb is regulated, in part, by reversible association with one of two HEXIMs and the 7SK snRNP. A recent proteomics survey revealed that P-TEFb and the HEXIMs are tightly connected to two previously-uncharacterized proteins, the methyphosphate capping enzyme, MEPCE, and a La-related protein, LARP7. Glycerol gradient sedimentation analysis of lysates from cells treated with P-TEFb inhibitors, suggested that the 7SK snRNP reorganized such that LARP7 and 7SK remained associated after P-TEFb and HEXIM1 were released. Immunodepletion of LARP7 also depleted most of the 7SK regardless of the presence of P-TEFb, HEXIM or hnRNP A1 in the complex. Small interfering RNA knockdown of LARP7 in human cells decreased the steady-state level of 7SK, led to an initial increase in free P-TEFb and increased Tat transactivation of the HIV-1 LTR. Knockdown of LARP7 or 7SK ultimately caused a decrease in total P-TEFb protein levels. Our studies have identified LARP7 as a 7SK-binding protein and suggest that free P-TEFb levels are determined by a balance between release from the large form and reduction of total P-TEFb.
Krueger
Brian J
BJ
Molecular and Cellular Biology Program, University of Iowa, Iowa City, Iowa, USA.
Jeronimo
Célia
C
Roy
Bibhuti Bhusan
BB
Bouchard
Annie
A
Barrandon
Charlotte
C
Byers
Sarah A
SA
Searcey
Courtney E
CE
Cooper
Jeffrey J
JJ
Bensaude
Olivier
O
Cohen
Eric A
EA
Coulombe
Benoit
B
Price
David H
DH
D002460:Cell Line; D015696:Gene Products, tat / Q000378:metabolism; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B / Q000378:metabolism; D006801:Humans; D042925:Positive Transcriptional Elongation Factor B / Q000378:metabolism*; D034622:RNA Interference; D012342:RNA, Small Nuclear / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D012261:Ribonucleoproteins / Q000032:analysis / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017411:Ribonucleoproteins, Small Nuclear / Q000378:metabolism*; D014157:Transcription Factors; D015533:Transcriptional Activation
D015696:Gene Products, tat; C476123:HEXIM1 protein, human; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; C528908:Larp7 protein, human; D012342:RNA, Small Nuclear; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear; D014157:Transcription Factors; D042925:Positive Transcriptional Elongation Factor B