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Results reveal that BZAP45 protein possesses a decapeptide as a part of the putative leucine-zipper protein with an ATP or GTP nucleotide binding fold. Data indicate that purified BZAP45 interacts with site II cell cycle control element indirectly in cooperation with H4 promoter.

The purification of the histone nuclear factor M has been achieved and it is found to be a protein with molecular mass of 48K which is the same as interferon regulatory factor 2 (IRF-2). The transcription of the human histone gene reaches a maximum limit during the early S phase. IRF-2 has an oncogenic action and there is a link between IRF-2 and a gene that is linked to DNA replication and the transition from G1 to S phase of cell cycle.

Previous studies have implicated the dynactin complex as a receptor or adaptor for cytoplasmic dynein on the surface of cargo. This interaction is mediated by the cytoplasmic dynein intermediate chains (ICs) and [p150.sup.Glued]. To identify regulatory mechanisms that control the binding of cytoplasmic dynein to cargo, we mapped phosphorylation sites on the ICs and [p150.sup.Glued], and determined the impact of phosphorylation on protein function. A [p150.sup.Glued] phosphorylation site was identified in the [NH.sub.2]-terminal 'head' domain through mapping of the epitope of a phospho-sensitive antibody. This phosphorylation site resides near the microtubule-binding domain of [p150.sup.Glued], and fits the consensus for cAMP-dependent PKA. Using GFP-fusions, we visualized site-directed mutants in living cells and determined that [p150.sup.Glued] phosphorylation regulates the dynamic targeting of dynactin to microtubule plus-ends. To test IC phosphorylation as a regulatory mechanism, we analyzed cytoplasmic dynein by 2-D gel analysis and detected two IC variants, one of which was eliminated by phosphatase treatment. To measure the effect of this IC phosphorylation on the IC-[p150.sup.Glued] interaction, we performed overlay assays and observed that [p150.sup.Glued] bound dephosphorylated but not phosphorylated ICs. To map the site of IC phosphorylation, we subjected the purified cytoplasmic dynein ICs to mass spectrometry. A single phosphorylated tryptic fragment was identified corresponding to the [p150.sup.Glued]-binding domain of IC-2C. Fragmentation and retention time analysis were used to map the phosphorylation site to serine 84. Site-directed mutants designed to mimic the dephosphorylated (S84A) or phosphorylated (S84D) IC disrupted both in vitro and in vivo IC phosphorylation. S84A mutants bound [p150.sup.Glued] in vitro and overexpression perturbed transport of dynein-dependent membranes. The S84D mutant diminished [p50.sup.Glued] binding in vitro and did not disrupt dynein-mediated transport when expressed in vivo. These findings represent the first evidence that IC phosphorylation plays a fundamental role in the binding of cytoplasmic dynein to dynactin and cargo. (Supported by AHA grant 3009N.)

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