Disease relevance of NAP1

• SNAP-1 expressed in Escherichia coli induces supercoiling in relaxed circular DNA, suggesting that SNAP-1 may have nucleosome assembly activity [1].
• Because the nucleosome assembly is performed separately from the DNA replication step, this system is more versatile and biochemically tractable when compared with nucleosome assembly during simian virus 40 (SV40) DNA replication [2].

High impact information on NAP1

• Recent data argue strongly that a protein complex termed chromatin assembly factor-1 (CAF-I) plays a major role in de novo nucleosome assembly during DNA replication [3].
• However, mechanistic links between histone acetylation and nucleosome assembly have not been established in vivo or in vitro [3].
• In this study, the MYST family acetyltransferase Sas2 was found to interact with Cac1, the largest subunit of Saccharomyces cerevisiae chromatin assembly factor-I (CAF-I), and with the nucleosome assembly factor Asf1 [4].
• Deletion of both tails, a lethal event, alters micrococcal nuclease-generated nucleosomal ladders, plasmid superhelicity in whole cells, and nucleosome assembly in cell extracts [5].
• We suggest that CAF-1 p150 has a heterochromatin-specific function distinct from its nucleosome assembly function during S phase [6].

Biological context of NAP1

• Our experiments also suggest that NAP1 is required for the ability of the Clb2/p34CDC28 kinase complex to amplify its own production, and that NAP1 plays a role in regulation of microtubule dynamics during mitosis [7].
• Together, these results demonstrate that NAP1 is required for the normal function of the activated Clb2/p34CDC28 kinase complex, and provide a step towards understanding how cyclin-dependent kinase complexes induce specific events during the cell cycle [7].
• This result suggests that yeast NAP1 is required for the maintenance of cumulative nucleosome formation in vivo and the loss of Nap1 leads to a change in the gene expression level in a cluster [8].
• Saccharomyces cerevisiae Ats1p interacts with Nap1p, a cytoplasmic protein that controls bud morphogenesis [9].
• These results are consistent with a role for plant NAP1-like proteins in cell division [10].

Anatomical context of NAP1

• The TATA box-binding transcription factor TFIID from Saccharomyces cerevisiae was tested for its ability to mediate regulatory factor functions both in a cell-free system reconstituted with other general initiation factors (purified from HeLa cells) and in a combined nucleosome assembly-transcription system [11].
• We have isolated from a human thymus cDNA library a cDNA clone encoding a potential protein with 54% amino acid similarity to that encoded by a previously identified cDNA for yeast nucleosome assembly protein I (NAP-I) [12].

Physical interactions of NAP1

• Our studies demonstrate that a highly conserved protein called Sda1 binds to Nap1 both in vitro and in vivo [13].
• Consistent with these phenotypes, mutant CAF-I complexes defective for PCNA binding displayed reduced nucleosome assembly activity in vitro but were stimulated by Asf1p-histone complexes [14].
• We demonstrate that Nap1p can bind directly to Kap114p, the primary karyopherin/importin responsible for the nuclear import of H2A and H2B [15].
• Affinity chromatography experiments demonstrate that Gin4 binds tightly to Nap1, indicating that the functions of these two proteins are closely tied within the cell [16].
• Quantitative comparisons with control plasmids ruled out the possibility that HSF was bound only to a small fraction of molecules that might have escaped nucleosome assembly [17].

Regulatory relationships of NAP1

• Our results suggest Ats1p might regulate coordination of the microtubule state with the cell cycle through an interaction with Nap1p [9].
• The results are consistent with the idea that the effects of the spt mutations on nucleosome assembly and/or stability activate repressors of HTA1 transcription [18].
• Furthermore, we demonstrate that Nap1p promotes the association of the H2A and H2B NLSs specifically with the karyopherin Kap114p [15].
• Transcription from constructs designed to create steric competition between binding of HSF and histone H2A-H2B dimers was generally poor, suggesting that nucleosome assembly precedes and inhibits HSF binding [19].

Other interactions of NAP1

• The stable maintenance of Nis1 was dependent on Nap1 [20].
• In Saccharomyces cerevisiae, additional functions have been ascribed to Nap1, as it has been shown to interact with Clb2 (B type cyclin) and Gin4 (septum formation) [8].
• We have examined the ability of the yeast mitotic cyclin Clb2 to function in cells that lack NAP1 [7].
• NAP1 acts with Clb1 to perform mitotic functions and to suppress polar bud growth in budding yeast [7].
• Consistent with this, we have found that Nap1 is required for viability in cells lacking the redundant G1 cyclins Cln1 and Cln2 [13].

Analytical, diagnostic and therapeutic context of NAP1

• We detected physical interaction between Nis1 and Nap1 in vivo by a co-immunoprecipitation experiment [20].
• Analytical ultracentrifugation was used to determine the association states of NAP1 alone and in complexes with core histones [21].
• We have used affinity chromatography to identify proteins that interact with Nap1, a protein previously shown to play a role in mitosis [13].
• Identification and molecular cloning of yeast homolog of nucleosome assembly protein I which facilitates nucleosome assembly in vitro [22].
• Purification, crystallization and preliminary X-ray diffraction analysis of yeast nucleosome-assembly factor Cia1p [23].

References