In vitro assembly of a functional human CDK7-cyclin H complex requires MAT1, a novel 36 kDa RING finger protein.

Abstract

It is proposed that the CDK7‐cyclin H complex functions in cell cycle progression, basal transcription and DNA repair. Here we report that in vitro reconstitution of an active CDK7‐cyclin H complex requires stoichiometric amounts of a novel 36 kDa assembly factor termed MAT1 (ménage à trois 1). Sequencing of MAT1 reveals a putative zinc binding motif (a C3HC4 RING finger) in the N‐terminus; however, this domain is not required for ternary complex formation with CDK7‐cyclin H. MAT1 is associated with nuclear CDK7‐cyclin H at all stages of the cell cycle in vivo. Ternary complexes of CDK7, cyclin H and MAT1 display kinase activity towards substrates mimicking both the T‐loop in CDKs and the C‐terminal domain of RNA polymerase II, regardless of whether they are immunoprecipitated from HeLa cells or reconstituted in a reticulocyte lysate. MAT1 constitutes the first example of an assembly factor that appears to be essential for the formation of an active CDK‐cyclin complex.

The malarial CDK Pfmrk and its effector PfMAT1 phosphorylate DNA replication proteins and co-localize in the nucleus

“…The present study demonstrates a further similarity to CDK7 by showing that PfMAT1 interacts with both Pfmrk and Pfcyc-1. Interaction with both the CDK and cyclin is believed to stabilize the trimeric complex [41]. The molecular architecture of PfMAT1 is highly similar to human MAT1 with a ring finger, coiledcoil and hydrophobic domain.…”

Regulation of RNA polymerase II activity by CTD phosphorylation and cell cycle control

“…Biochemical puri®cation identi®ed the major CAK activity in mammalian and Xenopus cell lysates as a trimeric protein complex composed of a catalytic subunit CDK7 (Fesquet et al, 1993;Poon et al, 1993;Solomon et al, 1993), its regulatory subunit cyclin H (Fisher and Morgan, 1994;Ma È kela È et al, 1994), and a third subunit MAT1 (meÂnage-a Á-trois-1). MAT1 stabilizes the interaction between CDK7 and cyclin H and bypasses the requirement for T-loop phosphorylation for CAK activity (Devault et al, 1995;Fisher et al, 1995;Tassan et al, 1995a).…”

Retinoid-suppressed phosphorylation of RARα mediates the differentiation pathway of osteosarcoma cells

“…RARa is a substrate for cyclin-dependent kinase (CDK)-CAK complex, which consists of the catalytic subunit CDK7 (Wu et al, 1994), the regulatory subunit cyclin H (Fisher and Morgan, 1994) and the assembly factor/targeting subunit MAT1 (Tassan et al, 1995). The S77 of RARa (RARaS77) is the main residue phosphorylated by CAK .…”