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Biomedical subjects

F F Becker

Publications and source records attributed to F F Becker.

At least 127 records · Page 7Linked to original sources
PubMed1980

Analysis of highly repeated DNA sequences of rat with EcoR1 endonuclease.

Cleavage of rat liver nuclear DNA with EcolR1 restriction endonuclease yields 14 discrete fragments ranging from 2300 to 93 base pairs in length, representing approx. 10.5% of the rat genome. Fragments of 1500, 180, and 93 base pairs are reiterated over 100 000 times; fragments of 2300, 880, 290, and 200 base pairs are reiterated over 20 000 times; the remaining fragments are present in over 1000 copies per genome. When compared to whole rate DNA, 11 were 1-5% richer in A . T base pairs and five were 1.5-2.5 times more methylated. From the criteria of the banding patterns in complete and incomplete digests, base composition and extent of methylation, none of these fragments appeared to be generated as oligomers of a basic shorter repeat. The reassociation of EcoR1 fragments was monitored on hydroxyapatite and by S1 nuclease treatment in order to assess band reiteration frequency and the possibility of interpersion or short internal repeats. The renaturation of the four smallest EcoR1 fragments gave no indication of short internal repeats from hyperpolymer formation nor interpersion with lower frequency sequences by size reduction after S1 nuclease treatment. Anomalous renaturation of several large fragments was observed, possibly due to internal repeats.

Animals↗
PubMed1980

Purification of a low molecular weight non-histone chromosomal protein.

A non-histone chromosomal proteins was extracted from rat liver chromatin with 0.35 M NaCl and purified more than 2758 times to near homogeneity by hydroxyapatite, gel filtration, and phosphocellulose chromatography. The final fraction was greater than 95% pure as judged by non-denaturing gel electrophoresis. The protein, designated loosely bound non-histone chromosomal protein 1, had an observed molecular weight of 15 700. This protein was demonstrated to increase the amount of RNA synthesized in a heterologous (Escherichia coli RNA polymerase) transcription system and, therefore, this activity was also used to monitor its purification. The availability of highly purified loosely bound non-histone chromosomal protein 1 will make possible an examination of its structural and/or functional role in chromatin.

Animals↗
PubMed1980

EcoRI-generated reiterated components of the rat genome. I. Sequence of two (92 and 93 bp) related DNA fragments.

The sequence of the 92 and 93 bp long, highly repetitive DNA fragments, isolated from EcoRI digested rat liver DNA, were determined. These fragments, designated 92 and 93, are found in equal abundance, 6.5 x 10(5) copies per haploid genome. J92 and J93 can be distinguished by their differential sensitivity to cleavage by HaeIII and HindIII, respectively, which cut the fragments at 75 and 57 bp from their mutually homologous 5'-ends. J92 and J93 are 38% and 35.4% G + C, respectively, and contain a disproportionate number of triplets complementary to stop codons in all reading frames. Three methylated sites were found in J92 while none could be detected in J93. The sequences around the m5C sites were 5'-Py-Py-m5C-G-Pu-Pu, except for one case where the second Py was replaced by an A. This site appeared to be hemimethylated. When J92 and J93 are placed in register from their mutually homologous 5'-ends, homology is 73% for the first 30 bp region and 63.5% for the total molecule. Thermal melting studies indicate sequence heterogeneity within J92 and J93 from substantial internal base mismatches. The sequences derived are therefore composite averages for the whole molecules. The Cot1/2 for the sequence was measured spectrophotometrically to be 2 x 10(-2) M/s on a DNA phosphorus basis and 2.15 x 10(-4) M/s on a mole fragment basis.

Animals↗
PubMed1980

Progressive DNA damage in hepatic nodules during 2-acetylaminofluorene carcinogenesis.

The method of alkaline elution was used to detect DNA alteration in rat liver throughout the carcinogenic sequence that resulted from exposure to a standard four-cycle feeding regimen of 2-acetylaminofluorene (AFF). At the end of 3 weeks of AAF feeding, DNA from aliquots of whole liver demonstrated a small but significant degree of damage. By the end of the fourth AAF feeding, the liver exhibited numerous nodules that could be dissected free from surrounding tissue. DNA from these putative premalignant lesions showed approximately 136% more damage than that seen at the end of 3 weeks of AAF feeding. Two to 4 months following the cessation of AAF, DNA from persistent nodules was examined for eivdence of alteration. Despite the prolonged absence of exposure to AAF, DNA damage was found to have progressed and was as much as 320% greater than that seen at the end of the first cycle. While the persistence of DNA damage during chronic exposure to a carcinogen has been reported previously, the observations that the DNA of a focal lesion which is putatively premalignant was damaged and, further, that this alteration progressed in the absence of a carcinogen, are unique.

2-Acetylaminofluorene↗
PubMed1980

Covalent binding of 2-acetylaminofluorene, 2-aminofluorene, and N-hydroxy-2-acetylaminofluorene to rat liver nuclear DNA and protein in vivo and in vitro.

Binding of the hepatocarcinogen 2-acetylaminofluorene (AAF) and two metabolites, 2-aminofluorene (AF) and N-hydroxy-2-acetylaminofluorene (N-OH-AAF), to the DNA and protein of rat hepatic nuclei was examined in vitro and in a cell-free system. Three and one-half hr following a single injection of each compound in equimolar amounts. DNA contained approximately 50% more of the compounds per mg than did protein. The amount of N-OH-AAF bound to DNA was 4 times greater than that of AAF, while AF bound in intermediate amounts. When incubated with nuclei in a cell-free system, AAF seldom bound in measurable amounts, while significant amounts of N-OH-AAF and AF bound to both DNA and protein. As occurred in vivo, DNA bound more of each per mg than did protein. The amount of N-OH-AFF bound to intranuclear DNA increased 54% when an aliquot of the postmicrosomal liver fraction was added to the incubation mixture, but maximum binding of AF occurred in the absence of any other liver fraction. Thus, it was shown that two AAF metabolites, AF and N-OH-AAF, bind covalently to the DNA and protein of hepatic nuclei more readily than does AAF itself and that binding in a cell-free system parallels binding in vivo. Additional evidence suggests that rat hepatic nuclei are capable of mediating the binding of AF and N-OH-AAF to macromolecules through distinct enzyme systems. This is the first demonstration that the nucleus is capable of metabolizing AF to an electrophile that can bind covalently to DNA.

2-Acetylaminofluorene↗
PubMed1980

Diminished hepatic binding protein for desialylated glycoproteins during chemical hepatocarcinogenesis.

The lectin hepatic binding protein has a specific binding capacity for desialylated serum glycoproteins and is limited to hepatocyte membranes. This binding capacity was reduced by approximately 60% in the neoplastic nodules which resulted from exposure of rat livers to N-2-acetylaminofluorene. The binding capacity of the primary hepatocellular carcinomas which resulted from this regimen was reduced by 95%. The loss of binding capacity was found to be proportional to the decreased concentration of immunologically detectable lectin in the altered tissues.

2-Acetylaminofluorene↗
PubMed1979

Alterations in chromosomal proteins in C3H/HeN mice with spontaneous primary hepatocellular carcinomas.

The chromosomal proteins from chromatins of normal and background liver and spontaneous primary hepatocellular carcinomas (PHC) of C3H/HeN mice were examined by high resolution acid-urea and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Before gel analysis, the histone and non-histone chromosomal proteins (NHCP) from the various tissues studied were separated by affinity chromatography. No qualitative or quantitative differences in histone content were detected in any of the chromatins studied. Tumor and background chromatins did, however, exhibit higher NHCP content than normal tissues. When NHCP were fractionated on SDS polyacrylamide gels, the appearance of 10 new unique NHCP, many of which were of high molecular weight, was found to accompany the manifestation of malignancy in these C3H/HeN mice. Conversely, the abundance of a number of individual NHCP decreased precipitiously in PHC chromatin; and, additionally, two high-molecular-weight NHCP present in normal chromatins were not detectable in background and PHC chromatin. A number of NHCP were found to be unique to each of the chromatins studied. The progressive increase in total number of NHCP in background and PHC chromatin when compared to normal chromatin suggested that such changes in NHCP might indicate progression towards malignancy. The acquisition of new high-molecular-weight NHCP, the loss of some high-molecular-weight NHCP, and the decrease in individual NHCP found for mouse PHC correlate well with findings of previous studies in other systems in which malignant transformation was induced with some agent. It appears then that changes in NHCP accompany both spontaneous and induced malignant transformation, and that such changes may reflect alterations in gene expression known to accompany malignancy.

Animals↗
PubMed1979

Analysis of chromosomal proteins of fractionated chromatin from rat liver and transplantable hepatocellular carcinomas.

The chromosomal proteins from a number of transplantable hepatocellular carcinomas (THC) induced by a single carcinogen or its derivatives and varying greatly in their growth rates were examined by sodium dodecyl sulfate (SDS) polyarcylamide gel electrophoresis. Before extraction and analysis of proteins, chromatin from hepatomas, as well as from normal and regenerating liver was fractionated into rapidly and slowly sedimenting gradient components. Ten non-histone chromosomal proteins (NHCP) present in the tumors and ranging in molecular weight from 220,000 to 55,000, were absent from normal liver. Further, each rapidly growing tumor possessed more non-histone protein bands in the most rapidly sedimenting chromatin fractions than did corresponding, slowly growing tumor fractions. A number of single protein occurrences common only to normal liver and/or rapidly or slowly growing tumors were also found. In contrast, NHCP banding patterns of rapidly growing 70% hepatectomized rat liver were identical to those of non-dividing liver. Of particular interest was the finding that the prototypic "minimal deviation tumor" 9618A varied more in its NHCP-banding pattern when compared to liver than did those tumors which were rapidly growing and poorly differentiated. These studies represent an initial attempt at seeking NHCP which might be uniquely related to the malignant process.

Animals↗
PubMed1979

Rhomboid flap in facial reconstruction. New concept of tension lines.

The rhomboid flap has become a popular reconstructive alternative for facial defects in recent years. Since the original description by Limberg, several modifications of the flap have been described, the most important of which was by Dufourmental. In the literature and at many soft-tissue courses, it has been taught that after rotation the maximum tension of the rhomboid flap is at the corner of the rhomboid most distant from the transposed flap. The author shows that the maximum tension of the flap is at the closure of the donor area. This phenomenon is amply illustrated with clinical cases. The Dufourmental modification is more satisfactory than the classical rhomboid flap in most cases because there is less tension on the closure. An understanding of these concepts is essential to the successful use of this important flap in order to avoid distortion of vital facial landmarks. I report a series of 30 consecutive rhomboid flaps.

Evaluation Studies as Topic↗
PubMed1979

In vivo binding of N-2-acetylaminofluorene and its N-hydroxy derivative to the DNA of fractionated rat liver chromatin.

The in vivo binding of radioactive N-2-acetylaminofluorene (AAF) and N-hydroxy-2-acetylaminofluorene (N-OH-AAF) to the DNA of rat liver chromatin was examined. The chromatin was fractionated into putative transcriptionally active and inactive fractions by hydrodynamic shearing and subsequent glycerol gradient centrifugation, DNAase II digestion followed by MgCl2 aggregation of transcriptionally inactive chromatin, or mild digestion with micrococcal nuclease. Carcinogens were administered for various times prior to sacrifice. Irrespective of the duration of exposure, no preferential binding of either carcinogen to DNA was detected in any of the fractions prepared by hydrodynamic shearing of DNAase II digestion. When micrococcal nuclease was utilized, a 2-fold increase in carcinogen bound to the DNA of that chromatin fraction containing the smallest molecular weight fragments was detected. These small molecular weight fragments produced by micrococcal nuclease have been postulated to be derived from in vivo transcriptional units. Additionally, when DNAase II was used to probe chromatin from rat livers which had been exposed to a carcinogenic regimen of AAF, no preferential binding of radioactive N-OH-AAF to the DNA of any chromatin fraction was detected.

2-Acetylaminofluorene↗
PubMed1979

Immunocytochemical localization of epoxide hydrase in hyperplastic nodules induced in rat liver by 2-acetylaminofluorene.

A knowledge of the biological characteristics of carcinogen-induced hyperplastic nodules of rat liver may be important in the understanding of cancer development. Although its biological role remains to be elucidated, the level of microsomal epoxide hydrase (epoxide hydrolase, EC 3.3.2.3) is 5- to 7-fold greater in hyperplastic nodules nodules induced by feeding the hepatocarcinogen 2-acetylaminofluorene than in liver of control rats. After removal of the carcinogen from the diet, the high level of the enzyme is maintained in those nodules that persist and in the hepatocellular carcinomas that subsequently develop. The availability of antibody to the epoxide hydrase made it possible to use electron microscopic immunocytochemistry to localize this enzyme in the cells of hyperplastic nodules. The immunocytochemical procedure provides direct visual evidence for the presence of this enzyme in smooth endoplasmic reticulum and also in rough endoplasmic reticulum (including the nuclear envelope) of the nodule's parenchymal cells.

2-Acetylaminofluorene↗
PubMed1979

Decreased fidelity of DNA polymerase activity during N-2-fluorenylacetamide hepatocarcinogenesis.

alpha and beta DNA polymerases (DNA nucleotidyltransferase; deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7) were isolated from nuclear and cytoplasmic fractions of rat livers exposed to a carcinogenic regimen with the hepatocarcinogen N-2-fluorenylacetamide and from 24-hr regenerating liver. The fidelity of polymerization of these enzymes was compared by determining the incorporation of noncomplementary deoxyribonucleoside triphosphates (misincorporation) on a poly(dA-dT).poly(dA-dT) template, with MnCl2 and MgCl2 as divalent cations. Our initial studies indicate that the cytoplasmic alpha polymerases from carcinogen-exposed rat livers were strikingly error-prone whereas the nuclear and cytoplasmic beta polymerases retained their fidelity throughout the feeding cycles. The misincorporation was significantly accentuated by MnCl2 compared with that obtained with MgCl2 as divalent cation. The products were sensitive to pancreatic DNase I digestion, indicating that the noncomplementary bases had been incorporated by the polymerization process. Nuclear alpha polymerase showed some degree of infidelity but less than that of cytoplasmic alpha polymerase.

2-Acetylaminofluorene↗
PubMed1979

Lack of proportionality between rate of cell division and induction of tumors in carcinogen-exposed regenerating livers.

Although a single pulse of dimethylnitrosamine administered during the regenerative response of liver subsequent to 70% hepatectomy resulted in more primary hepatocellular carcinomas in treated livers than in controls, the response was not proportionate to the level of cell division. Further, the use of 55-g male Sprague-Dawley rats that displayed an extremely active regenerative response did not significantly shorten the lag period before the appearance of tumors. Of additional interest was the finding that the post-S period might be even more susceptible to dimethylnitrosamine than the S phase was. These results support the suggestion that many aspects of the interaction between carcinogens and dividing cells and the requirement for subsequent events for the development remain unclear.

Animals↗