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R H Reeder

Publications and source records attributed to R H Reeder.

At least 91 records · Page 5Linked to original sources
PubMed1977

Immunological cross-reaction between calf and Drosophila histones.

Antibodies elicited by purified calf thymus histone fractions are used to quantitate the immunological cross-reactions between calf and Drosophila histones. The index of dissimilarity between calf and Drosophila histones are: H4, 1.0; H2B, 1.0; H3, 1.6; H2A, 2.0; H1, 16. These values respectively correspond to 0, 0, 4, 6, and 27% difference in amino acid composition. The differences in amino acid composition assessed by immunological techniques are in agreement with values obtained by amino acid analysis (Alfageme, C. R., Zweidler, A., Mahowald, A., and Cohen, L. H. (1974) J Biol. Chem. 249, 3729-3736 and Oliver, D., and Chalkley, R. (1972) Exp. Cell. Res. 73, 295-302). The strong immunological cross-reaction between calf and Drosophila histones H4, H3, H2A, and H2B leads us to suggest that antibodies elicited against purified histone fractions derived from calf thymus can serve as "universal" reagents for various studies of chromatin-bound histones. The use of standard preparations of antisera will facilitate comparisons of results obtained in different laboratories with various experimental systems.

Amino Acids↗
PubMed1977

Sites of transcription initiation in vivo on Xenopus laevis ribosomal DNA.

We report the results of a novel method for locating sites of transcription initiation using a complex of capping enzymes from vaccinia virions that catalyze the reaction pppG + S-adenosylmethionine + (p)ppXpYpZp..... -->(7m)GpppXpYpZp..... [Ensinger, M. J., Martin, S. A., Paoletti, E. and Moss, B. (1975) Proc. Natl. Acad. Sci. USA 72, 2525-2529]. This enzyme complex will cap di- or triphosphate termini but will not cap monophosphate or hydroxyl termini. Xenopus laevis 40S precursor rRNA from oocytes is capped by these enzymes, and we conclude that it has 5'-polyphosphate termini. Therefore, 40S RNA must represent the primary transcript of amplified X. laevis ribosomal DNA. The majority of 40S molecules with polyphosphate termini begin with the sequence (p)ppAAG. There is evidence, however, that the 5' terminus may be heterogeneous. The majority of all detectable initiation events were localized close to the region coding for the 5' end of the 40S RNA. No initiation sites were detected in the nontranscribed spacer, but an apparent initiation site in the middle of the transcribed region was also observed.

Animals↗
PubMed1976

Iodination of Xenopus laevis histone F2a1 in chromatin.

The reaction of calf thymus and Xenopus laevis histones with radioactive iodine has been studied under various conditions that affect chromatin structure. All histones from both species contain at least one tyrosine residue and, in a denaturing solvent, all the the histones react with iodine. Histone F2a1 has been studied in detail. Calf thymus F2a1 is known to contain four tyrosyls and all four react with iodine. In high voltage paper electrophoresis, the tyrosine-containing peptides from calf co-migrate with those from Xenopus F2a1, suggesting that the amino acid sequence is strongly conserved between these two species. Therefore, the published calf thymus F2a1 sequence has been used to order the Xenopus F2a1 peptides within the molecules. When gently isolated native chromatin is iodinated in a low ionic strength medium 60% of the radioactivity in F2a1 is in tyrosyl 88, 30% in tyrosyl 51, and tyrosyl 72 and 98 have almost no radioactivity. Reagents which remove the protein from the DNA (2 M NaCl) or partially disrupt protein tertiary structure (5 M urea) increase the reactivity of each of the four tyrosyls five- to tenfold, suggesting that all four are protected about equally by the overall folding of the chromatin. Isolated F2a1 iodinated in the presence of 10 M urea shows uniform labeling in each of the four peptides, suggesting that tyrosyl 72 and 98 are afforded some protection solely by protein-protein interactions. The stepwise removal of histones in increasing NaCl concentrations differentially increases the availability of each F2a1 tyrosyl. The preferential exposure of tyrosyl 88 coincides with the removal of the majority of F1 histones at 0.5 M NaCl while the gradual and stepwise increase in reactivity of tyrosyl 51, 72, and 98 correlates with the gradual removal of histones other than F1. Radioactive iodination of chromatin has been shown to be a sensitive probe for detecting changes in the association state (or conformation) of histone F2a1.

Amino Acid Sequence↗
PubMed1976

The 5' leads to 3' polarity of the Xenopus Ribosomal RNA precursor molecule.

Evidence is presented that in Xenopus laevis the 18S rRNA sequence is proximal to the 5' end of the rRNA precursor molecule and the 28S secquence is proximal to the 3' end. This assignment was made by digesting amplified ribosomal gene transcription complexes with EcoRI restriction endonuclease and spreading the cleaved transcription complexes for electron microscopy. From the known location of the EcoRI cutting sites within the transcribed region and the length of nascent chains on the cleaved transcription complexes, it was possible to make an unambiguous assignment of polarity.

Animals↗
PubMed1975

Histone gene arrangement in the sea urchin, Strongylocentrotus purpuratus.

The DNA coding for histones from Strongylocentrotus purpuratus, purified up to 100-fold with the use of Hg+2-CS2-SO4 and actinomycin-CsC1 equilibrium density gradients, has been used to study the clustering of genes coding for different histones and the size of the repeating multigene cluster. When digested with EcoRI restriction endonuclease, the histone DNA is identified in two classes of fragments with molecular weights of 1.15 X 106 and 2.8 X 106, whereas after treatment of the DNA with HindIII restriction endonuclease, histone gene sequences can be identified only in a fragment of 3.95 X 106. Treatment of the DNA with both enzymes simultaneously shows that there is a HindIII site within the smaller EcoRI fragment. Partial digests with HindIII give fragment sizes that appear to be simple multiples of a 3.95 X 106 repeat. Individual histone mRNAs all hybridize to the 3.95 X 106 fragment but only to one or the other EcoRI fragments. The evidence strongly suggests a repeating unit of 3.95 X 106 containing the genes for most, if not all, the histonrs.

Animals↗
PubMed1974

Amplified ribosomal DNA from Xenopus laevis has heterogeneous spacer lengths.

Eco R(1) restriction endonuclease makes two cuts in each repeating unit of amplified ribosomal DNA (rDNA) from Xenopus laevis. The locations of these cuts have been established by comparison of the secondary structure of single-stranded Eco R(1) fragments (as visualized in the electron microscope) with that of X. laevis rRNAs and of long strands of uncut rDNA. Of the two classes of fragments generated, the smaller one contains 90% of the 28S rRNA gene, has a duplex molecular weight of 3.0 x 10(6) and is homogeneous in size. The larger class of molecules contains 80% of the 18S rRNA gene and all of the nontranscribed spacer. These latter fragments are heterogeneous with molecular weights ranging from 4.0 to 5.9 x 10(6). The distribution of sizes within the large class of fragments varies among different preparations of rDNA, and heterogeneity is present in the DNA amplified from the rDNA of a single nucleolar organizer. The heterogeneity is located in the nontranscribed spacer region which is variable in length. This has been demonstrated by the formation of deletion loops in heteroduplexes made between larger fragments of different lengths.

Animals↗