The Myc-associated zinc finger protein MAZ is a transcription factor that participates in both the initiation and termination of transcription of target genes. MAZ functions as a true transcriptional repressor in that it represses transcription independent of the c-Myc promoter. Both MAZ and SP1 bind to the parathyroid hormone (PTH)/ PTH-related peptide receptor promoter, thereby influencing the cell-specific expression of its gene product. MAZ and SP1 also regulate expression from the serotonin 1A receptor gene promoter, suggesting that MAZ may act on a variety of promoters through G-C rich sequences, which serve as binding sites for the SP1 family of transcription factors. Competition between SP1 and MAZ control tissue-specific expression of the PNMT gene. The interaction of MAZ with the transcriptional repressor FAC1 may affect gene regulation in neurodegeneration. MAZ also acts as a growth suppressor protein, in part by affecting the levels of key cell cycle regulatory proteins such as cyclin A and E.