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MRG15, a novel chromodomain protein, is present in two distinct multiprotein complexes involved in transcriptional
Patricia S Pardo1, James K Leung, John C Lucchesi
1Roy M. and Phyllis Gough Huffington Center on Aging, Baylor College of Medicine, Houston, Texas 77030, USA.
Abstract:
MRG15 is a novel chromodomain protein that is a member of a family of genes related to MORF4. MORF4 (mortality factor on chromosome 4) induces senescence in a subset of human tumor cell lines. Our previous results indicated that MRG15 (MORF-related gene on chromosome 15) could derepress the B-myb promoter by association with Rb. In this study, sucrose gradient analysis demonstrated that MRG15 was present in two distinct nuclear protein complexes, MAF1 (MRG15-associated factor 1) and MAF2. Rb was associated with MRG15 and PAM14 (a novel coil-coil protein) in MAF1, and a histone acetyl transferase, hMOF, was an MRG15 partner in MAF2. Analysis of deletion mutants of MRG15 indicated that the leucine zipper at the C-terminal region of MRG15 was important for the protein associations in MAF1 and that the N-terminal chromodomain was required for the assembly of the MAF2 protein complex. Consistent with these data was the fact that a histone acetyltransferase activity associated with MRG15 was lost when the chromodomain was deleted and that both mutant MRG15 proteins failed to activate the B-myb promoter. The various mechanisms by which MRG15 could activate gene transcription are discussed.
Insights
MRG15 protein interacts with Rb and hMOF in distinct nuclear complexes, MAF1 and MAF2. These interactions are crucial for MRG15
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- MRG15 (MORF-related gene on chromosome 15) is a chromodomain protein linked to MORF4.
- MORF4 family genes are implicated in inducing senescence in human tumor cells.
- Previous studies suggest MRG15 can derepress the B-myb promoter via Rb association.
Purpose of the Study:
- To investigate the protein complexes and functional domains of MRG15.
- To elucidate the mechanisms by which MRG15 regulates gene transcription.
Main Methods:
- Sucrose gradient analysis to identify MRG15-associated nuclear complexes.
- Analysis of MRG15 deletion mutants.
- Assays for histone acetyltransferase activity and promoter activation.
Main Results:
- MRG15 exists in two nuclear complexes: MAF1 (with Rb and PAM14) and MAF2 (with hMOF).
- The C-terminal leucine zipper of MRG15 is essential for MAF1 association; the N-terminal chromodomain is vital for MAF2 assembly.
- Deletion of the chromodomain abolished histone acetyltransferase activity and B-myb promoter activation.
Conclusions:
- MRG15's function in gene transcription regulation is mediated by distinct protein complexes.
- Specific domains of MRG15 are critical for its interactions and associated activities.
- MRG15's role in B-myb promoter activation is dependent on its complex formation and histone acetyltransferase activity.