Mcm1 Promotes Replication Initiation by Binding Specific Elements at Replication Origins

Abstract

Replication of DNA must be inherently accurate and precisely regulated. It is therefore not surprising that the mechanism for the initiation of DNA replication is both complex and conserved. Initiation of DNA synthesis involves the assembly of a multicomponent complex at designated sites known as replication origins. While the protein components of the prereplication complex (pre-RC) used in this initiation process are conserved in all eukaryotes (5), there is little in common between the nucleotide sequences of replication origins within each eukaryote and between different eukaryotes (29).In Saccharomyces cerevisiae, replication origins (ORI) consist of defined sequences of about 200 bp that can replicate autonomously independently of their native chromosomal environment. These autonomously replicating sequences (ARSs) are modular in structure. They contain a ubiquitous 11-bp (5Ј-WTTTAYRTTTW) ARS consensus sequence (ACS) (11,22,63) where the origin recognition complex (ORC) binds (4). In certain ARSs, a 10-of-11 match of the ACS is sufficient for ORC recognition (64). The ACS is essential but not sufficient for autonomous replication. cis elements on the 5Ј (C domain) or the 3Ј (B domain) flanking sequences of the ACS are also required (12). Elements in the B domain of one particular ARS, ARS1, have been characterized in great detail. Three elements, known as B1, B2, and B3, have been identified (44). B1 is protected by the ORC (55), whereas B3 is protected by Abf1 (41) or Mcm1 (17) in in vitro footprinting analyses. Initiation of DNA synthesis at ARS1 has been mapped to a region between the B1 and B2 elements (6). Two of the three B elements in combination with the ACS are sufficient to promote autonomous replication. Although B elements of different ARSs are not conserved in nucleotide sequence, they are interchangeable between certain ARSs (31, 54, 61). The differences in size and modular composition of replication origins suggest that there are many ways to assemble a functional replication origin from a finite set of modules (60)(61)(62)65). The plasticity in the organization of replication origins is further illustrated by the dispensability of the B elements altogether in the presence of the C domain in several telomeric ARSs (13). However, because the C domain is generally larger, elements in the C domain have not been characterized.The redundant functions of the B and C domains in promoting replication initiation suggest that although the process of pre-RC assembly may be conserved, there are many ways to create an environment conducive to this assembly process. The concept of alternative pathways for creating an environment for pre-RC assembly is especially appealing in higher eukaryotes, where there appears not to be a unifying mechanism for site selection for pre-RC assembly. In Xenopus oocytes, replication initiation occurs at random sequences (38). In mammalian cells, initiation occurs at multiple sites within replication zones that are defined by their chromosomal contexts rather than nucleotide...

Programming Smooth Muscle Plasticity With Chromatin Dynamics

“…The original biological function of SRF appears to be that of a generic DNA-binding transcriptional activator important for expansion of cell populations, as the yeast SRF homolog MCM1 regulates DNA synthesis via binding DNA sequences near replication origins and by transcriptional activation of several cell-cycle control genes important for proliferative growth of this organism. 8 Indeed, this function has been evolutionarily conserved as SRF was so named because it was first found to regulate transcription of immediate early genes important for initiation of mitogenesis in response to the addition of serum into the media of various cultured mammalian cell lines. 9 It has been appreciated for quite some time that SRF homodimers perform this function via binding to CArG box DNA sequences within the promoters of immediate early genes (eg, c-fos) and forming a ternary complex with various serum-activated Ets-domain proteins (ie, the ternary factors [TCFs] Elk-1, Sap-1, Fli-1) that assist SRF in stimulating transcription of these genes.…”

The requirement of yeast replication origins for pre-replication complex proteins is modulated by transcription

“…Therefore, it is only in combination that the A, B1 and B2 elements from ARS121 are sufficient to reduce the requirement for Mcm2–7 protein function. Binding sites for the Mcm1 transcription factor have been suggested to affect mcm sensitivity (49). We found that mutating three Mcm1 binding sites outside this region (Yp-CN13) did not significantly elevate the plasmid loss rate in mcm2-1 cells (data not shown), consistent with the finding that the resilience of ARS121 to reduced Mcm2–7 function is linked mainly to the A, B1 and B2 elements.…”

“…This phenotype could result from the role of Mcm1 in regulating the expression of pre-RC genes, including CDC6 , MCM3 , MCM5 , MCM6 and MCM7 (56–58), or via a direct role for Mcm1 in pre-RC assembly (49). …”

Functional Taxonomy of Bacterial Hyperstructures

“…Coupling via enzyme messengers probably also exists between replication hyperstructures and metabolic hyperstructures. In the yeast Saccharomyces cerevisiae, thousands of genes, including those involved in DNA replication, show periodic expression during an ultradian respiration/reduction cycle, while the S phase occurs during the reduction period of the cycle (121,263) and its completion strictly depends on glyceraldehyde-3-phosphate dehydrogenase through its role in stimulating the expression of histone genes (292); moreover, a key protein in replication, MCM1, is linked genetically to several glycolytic enzymes (44,46). In human cells, lactate dehydrogenase, phosphoglycerate kinase, and glyceraldehyde-3-phosphate dehydrogenase can be transported to the nucleus, where they can bind single-stranded DNA and, in vitro, modulate the activity of the replicative DNA polymerases Pol␣, Pol␦, and Polε (218,231,240); moreover, phosphoglycerate kinase is a cofactor of Pol␣ (108).…”