Bleomycin mediated degradation of DNA-RNA hybrids does not involve C-1' chemistry.

Incubation of Fe(II) bleomycin and O2 with a number of 'A'-like DNA-RNA hybrid homopolymers at 4 atm O2 results in formation of base propenal and base in a ratio of approximately 1.0:1.0. This ratio differs dramatically from the corresponding ratio of approximately 10:1.0 observed when activated BLM degrades 'B'-like DNA homopolymers. Experiments were undertaken to determine if the shift to enhanced base production observed in the A-like hybrids is the result of C-1' chemistry in addition to the C-4' chemistry normally observed with B-like DNA under identical conditions. Increased accessibility of the 1'-hydrogen might be anticipated due to widening of the minor groove in the A-like conformers. Experiments using poly([1'-3H]dA) poly(rU) and poly([U-14C]dA) poly(rU) indicated that neither 3H2O nor deoxyribonolactone accompanied adenine release. In addition, studies using poly([4'-2H]dA) poly(rU) and poly([1'-2H]dA) poly(rU) unambiguously establish that the altered base to base propenal ratio is not the result of C-1' chemistry, but a direct consequence of C-4' chemistry.     

Chemical modifications of transfer RNA species. Transfer RNA's terminating in 2'- and 3'-O-methyladenosine

The preparation of transfer RNA's terminating in 2′- and 3′-$\text{O}$-methyl-adenosine has been undertaken by a combination of chemical and enzymatic techniques to permit a determination of the mechanism of tRNA aminoacylation. Neither of the two synthetic tRNA's was aminoacylated substantially in the presence of aminoacyl-tRNA synthetases, consistent with the hypothesis that the aminoacyladenylate moiety exists in the form of a species with considerable orthoester character.     

Positions of multiple insertions in SSU rDNA of lichen-forming fungi

Lichen-forming fungi, in symbiotic associations with algae, frequently have nuclear small subunit ribosomal DNA (SSU rDNA) longer than the 1,800 nucleotides typical for eukaryotes. The lichen-forming ascomycetous fungus Lecanora dispersa contains insertions at eight distinct positions of its SSU rDNA; the lichen-forming fungi Calicium tricolor and Porpidia crustulata each contain one insertion. Insertions are not limited to fungi that form lichens; the lichen ally Mycocalicium albonigrum also contains two insertions. Of the 11 insertion positions now reported for lichen-forming fungi and this ally, 6 positions are known only from lichen-forming fungi. Including the 4 newly reported in this study, insertions are now known from at least 17 positions among all reported SSU rDNA sequences. Insertions, most of which are Group I introns, are reported in fungal and protistan lineages and occur at corresponding positions in genomes as phylogenetically distant as the nuclei of fungi, green algae, and red algae. Many of these positions are exposed in the mature rRNA tertiary structure and may be subject to independent insertion of introns. Insertion of introns, accompanied by their sporadic loss, accounts for the scattered distribution of insertions observed within the SSU rDNA of these diverse organisms.      

Fluoride, pyrophosphate, and base release from 2'-deoxy-2'-fluoronucleoside 5'-diphosphates by ribonucleoside-diphosphate reductase

Ribonucleoside-diphsophate reductase from Escherichia coli catalyzes release of fluoride, inorganic pyrophosphate, and base from 2'-deoxy-2'-fluoronucleoside diphosphates. This reaction is accompanied by inactivation of the enzyme and an increase in absorbance at 314 nm of the inactivated protein. 2'-Deoxy-2'-fluoroadenosine 5'-diphosphate requires two turnovers per inactivation, whereas 2'-deoxy-2'-fluorocytidine 5'-diphosphate requires 100 turnovers per inactivation.