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Research has been conducted on the Yph1p, a protein containing a BRCT domain. The identification of the Saccharomyces cerevisiae interacting proteins has been carried out via the origin recognition complex immunopresipitation and the results indicate that Yph1p is present in multiprotein complexes.

Research has been conducted on the DNA polymerases which require tethering to the accessory factor, a ring-shaped clamp, to bind to DNA during replication. The authors review the structural studies on loading these clamps onto DNA by the clamp loader machine.

Research shows that FASCIATA1 and FASCIATA2 genes maintain cellular and functional organization of the shoot and root apical meristems in Arabidopsis. Data indicate that the FASCIATA gene products are analogous to chromatin assembly factor-1, which helps maintain stability of gene expression status during the apical meristems postembryonic development.

The novel protein p62(super dok) was purified from a hematopoietic cell line expressing the chimeric p210(super bcr-abl) protein which is usually found in chronic myelogenous leukemia. A unique feature of the p62(super dok) protein is the presence of a signaling molecule. Association of p62(super dok) with the GTPase-activating protein correlated with its tyrosine phosphorylation. p62(super dok) is rapidly tyrosine-phosphorylated upon activation of the c-Kit receptor, indicating it to be a component of a signal transduction pathway downstream of receptor tyrosine kinases.

A chromatin assembly complex (CAC) that contains chromatin assembly factor 1 (CAF-1) and the posttranslationally modified histones H3 and H4 is discovered and characterized. A cDNA for p48, the small subunit of CAF-1 and a member of a highly conserved subfamily of WD-repeat proteins, is cloned. Experiments show that the CAC plays a key role in the de novo nucleosome assembly pathway and that the p48 subunit participates in other aspects of histone metabolism.

A model system is designed with the Xenopus egg extracts and human cell extracts to examine DNA repair and chromatin assembly. In the former, repair of lesions occurs on an ultraviolet-treated plasmid together with chromatin assembly. A complementation assay is also demonstrated with human cell extracts that support DNA repair, with the incapacity for chromatin assembly remedied by Xenopus extract. The human chromatin assembly factor 1, which is responsible for the specificity of replicating DNA assembly, also supports chromatin assembly of repaired DNA.

The origin recognition complex 1 protein (Orc1p) of Saccharomyces cervisiae is structurally similar to Cdc6p, Cdc18p, and Sir3p. The yeast proteins Cdc6p and Cdc18p control DNA replication. The region of Orc1p that are similar to Cdc6p probably signals the initiation and completion of transcription. Sir3p controls transcription silencing of the mating-type loci. The N-terminal domain regions, that bind to histones and the regions required for protein localization, are similar in Orc1p and Sir3p.

The human chromatin assembly factor I(CAF I), is a protein complex having three subunits, p150, p60 and p50, which bind newly synthesized histones onto DNA replication sites indicating that these complexes are intermediates between histone synthesis and assembly onto replicating DNA. In eukaryotic organisms, the DNA is packed in the nucleus with a number of proteins to form a nucleoprotein structure, the chromatin. Of the three subunits in the CAF I protein, p150 and p60 are essential for chromatin assembly activity whereas p50 is uncertain.

Byline: Paul D. Kaufman, Ryuji Kobayashi, Naama Kessler, Bruce Stillman Abstract: Chromatin assembly factor I (CAF-I) from human cellnuclei is a three-subunit protein complex that assembles histone octamers onto replicating DNA in a cell-free system. Sequences of cDNAs encoding the two largest CAF-I subunits reveal that the p150 protein contains large clusters of charged residues, whereas p60 contains WD repeats. p150 and p60 directly interact and are both required for DNA replication-dependent assembly of nucleosomes. Deletion of the p60-binding domain from the p150 protein prevents chromatin assembly. p150 and p60 form complexes with newly synthesized histories H3 and acetylated H4 in human cell extracts, suggesting that such complexes are intermediates between histone synthesis and assembly onto replicating DNA. Author Affiliation: Cold Spring Harbor LaboratoryCold Spring Harbor, New York 11724, USA

A study of DNA replication in origin recognition complex (ORC) mutants binding to Saccharomyces cerevisiae under specific temperature conditions revealed that temperature influences the rate of replication in wild-type cells, orc2-1 ad orc5-1, with rate of replication decreasing as temperature increases. Use of genetic screening indicated CDC6 as the multicopy suppressor of orc5-1, 2-D gel and biochemical analyses suggested an interaction between Cdc6p and ORC.

Identification and characterization of the proteins that replicate genomes of bacteriophage T4 and Escherichia coli reveal that the protein apparatus is capable of monitoring progress in different molecular processes and detecting abnormalities. The functions of these proteins are conserved even after replication in both prokaryotes and eukaryotes.