Multiple Phosphorylated Forms of the Saccharomyces cerevisiae Mcm1 Protein Include an Isoform Induced in Response to High Salt Concentrations

Abstract

The Saccharomyces cerevisiae Mcm1 protein is an essential multifunctional transcription factor which is highly homologous to human serum response factor. Mcm1 protein acts on a large number of distinctly regulated genes: haploid cell-type-specific genes, G 2 -cell-cycle-regulated genes, pheromone-induced genes, arginine metabolic genes, and genes important for cell wall and cell membrane function. We show here that Mcm1 protein is phosphorylated in vivo. Several (more than eight) isoforms of The Saccharomyces cerevisiae MCM1 gene encodes an essential DNA-binding protein that is apparently multifunctional. Mutations in MCM1 affect autonomously replicating sequencespecific minichromosome maintenance, recombination, chromosome segregation, and haploid cell-type-specific gene expression (17,18,33,35,46,67). In addition, potential target genes of Mcm1 protein encode proteins involved in cell cycle regulation (G 1 and G 2 ), cell wall and membrane integrity, cellular metabolism, and stress tolerances (41,43,52). Based on the diversity of this group of genes, we suggested that Mcm1 protein acts as a global regulator that could play a role in cell cycle control (41). The essential involvement of Mcm1 protein in G 2 control of the cell cycle was demonstrated recently: depletion of Mcm1, which is required for expression of G 2 -cell-cycle-regulated genes SWI5 (43) and CLB2 (45), results in cell cycle arrest at G 2 and defects in transcription of many G 2 -cell-cycle-specific genes (2).The primary biochemical functions of Mcm1 protein are its sequence-specific DNA-binding activity and interactions with gene-specific cofactors that also recognize specific DNA sequences. An 80-amino-acid DNA-binding domain of Mcm1, which is 75% identical to the human serum response factor (SRF), is essential as well as minimally sufficient for known Mcm1 functions; this domain is located in the N-terminal portion of Mcm1 protein (residues 18 to 97) (9,13,71). In this essential domain the N-terminal 56 amino acids, called the MADS box, are highly conserved in a family of proteins, most of which are transcription factors involved in cellular development and differentiation (see Fig. 1) (reviewed in reference 79). These amino acids are involved in sequence-specific DNA binding and dimerization (10,61,69,77,90). The C-terminal 24 amino acids of the domain are involved in protein-protein interactions, both within the dimer (in addition to MADS box interactions) and with other proteins, such as gene-specific cofactors and possibly the transcription apparatus (9, 10, 57, 69). Mcm1 protein also contains a 17-amino-acid N-terminal extension, as well as an acidic stretch and a glutamine-rich domain in the carboxyl two-thirds of the protein. Although these domains are dispensable for viability (9,13,71), at least one of them, the acidic domain, has been implicated in the modulation of a specific Mcm1 function, ␣-cell-type-specific gene expression (13).Mcm1 protein recruits specific cofactors to different types of genes at which it acts. The type of reg...

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Genome-wide expression screens indicate a global role for protein kinase CK2 in chromatin remodeling

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