The NH2-terminal extension of high molecular weight forms of basic fibroblast growth factor (bFGF) is not essential for the binding of bFGF to nuclear chromatin in transfected NIH 3T3 cells.

Immunolocalization of basic fibroblast growth factor (bFGF) was investigated in NIH 3T3 cells transfected with a cDNA encoding for the 18 kD form of human bFGF (18 kD-bFGF) or with a bFGF cDNA encoding for both 18 kD-bFGF and NH2-terminal extended high molecular weight forms of bFGF (HMW-bFGFs). Nuclear and cytoplasmic bFGF-immunoreactivity was observed in both transfectants. Nuclear bFGF immunoreactivity was evenly distributed during interfase and associated with condensed chromosomes throughout the mitotic cycle. Cell fractionation, followed by Western blot analysis, confirmed the presence of 18 kD-bFGF and of HMW-bFGFs in the nucleus of transfected cells. Also, both 18-kD bFGF and HMW-bFGFs copurified with nuclear chromatin. After trypsin digestion, chromatin-bound bFGFs showed a rapid degradation of the nuclear-targeting NH2-terminal extension of HMW-bFGFs which were converted to the 18 kD form. On the contrary, 18 kD-bFGF appeared to be trypsin-resistant when bound to nuclear chromatin or to isolated eukaryote DNA. Thus, our data indicate that: i) both 18 kD-bFGF and HMW-bFGFs localize into the nucleus of transfected NIH 3T3 cells and bind to nuclear chromatin; ii) the interaction of all bFGF isoforms with nuclear chromatin is mediated by one or more sequences present within the 18 kD form; iii) the chromatin-binding domain of HMW-bFGFs is distinct from their nuclear-targeting domain.

Liver genotoxic activity of an epoxide derivative of the hepatocarcinogenic beta-blocker DL-ZAMI 1305.

A single administration of the sex-dependent hepatocarcinogenic beta-blocker DL-1-(2-nitro-3-methyl-phenoxy)-3-tert-butylamino-propan-2-ol (DL-ZAMI 1305) induces dose-dependent liver DNA damage, as evaluated by alkaline sucrose gradient analysis, in female but not in male Fisher 344 rats. A single administration of the direct mutagenic epoxide-derivative of DL-ZAMI 1305 3-methyl-2-nitro-1-(2,3-epoxypropoxy)-benzene induces dose-dependent DNA damage in the liver of animals of both sexes. However, also in this case, the genotoxic activity of the compound appears to be significantly higher in female than in male rats. A DNA-damaging capacity similar in the two sexes is instead exerted by DL-ZAMI 1305-unrelated direct mutagens, like N-methyl-N-nitrosourea (MNU) and methyl-methanesulfonate (MMS). The data confirm the sex-dependent susceptibility of rat liver to the genotoxic activity of DL-ZAMI 1305-related molecules, also in the absence of an absolute requirement for a metabolic activation of the compound.

Calf thymus DNA polymerase delta: purification, biochemical and functional properties of the enzyme after its separation from DNA polymerase alpha, a DNA dependent ATPase and proliferating cell nuclear antigen.

We have established a novel procedure to purify calf thymus DNA polymerase delta from cytoplasmic extracts. The enzyme has typical properties of DNA polymerase delta including a 3' - greater than 5' exonuclease activity and efficiently replicates natural occurring genomes such as primed single-stranded M13 DNA and single-stranded porcine circovirus DNA, this last one thanks to an associated or contaminating primase activity. A processivity of at least a thousand bases was evident and this in the apparent absence of proliferating cell nuclear antigen. The enzyme was purified through a procedure that allows the simultaneous isolation of DNA polymerase delta, DNA polymerase alpha-primase and a DNA dependent ATPase. All these enzymes coeluted from a phosphocellulose column. After chromatography on hydroxylapatite DNA polymerase delta separated from the coeluting DNA polymerase alpha and DNA dependent ATPase. Separation of the latter two was achieved on heparin-Sepharose. DNA polymerase delta was further purified by heparin-Sepharose and fast protein liquid chromatography. Purified DNA polymerase delta was resistant to the DNA polymerase alpha inhibitors BuPdGTP and BuAdATP and did not react with DNA polymerase alpha monoclonal and polyclonal antibodies. Based on this isolation protocol we can start to test biochemically the hypothesis whether DNA polymerase delta and DNA polymerase alpha might act coordinately at the replication fork as leading and lagging strand replicases, respectively.