A highly variable region of chloroplast DNA has been analyzed from three isolates of Oenothera hookeri strain Johansen. The variability results from the presence of two, four or seven copies of a discrete 24-base pair tandem repeat in a segment of the chloroplast DNA within the inverted repeat. Alignment of this DNA region with the published tobacco cpDNA sequence shows that in Oenothera, the repeats are insertions within a large unidentified reading frame, with each repeat unit specifying an eight amino acid in-frame addition. A model to explain the frequent alterations in the copy number of this 24-bp unit is proposed: imprecise alignment and recombination between the two large inverted repeats followed by copy correction could result in an amplification or deletion of the 24-bp segments.
Evolutionary relationships of four plastid genomes (plastomes) from different Oenothera species have been assessed by sequence comparisons of two intergenic regions that separate the ribosomal protein genes rpl16, rpl14, and rps8. Sequence changes include base substitutions, the occurrence of a 29-base tandem duplication, and variation in the length of two poly-A stretches. Additions/deletions in chloroplast DNA may not be useful for evolutionary comparisons more distant than these, particularly if the sequences undergo divergence after the initial event, but the length mutations reported here allow a finer resolution of the phylogeny of the closely related Oenothera plastomes than would have been possible if only base substitutions had been considered. Comparisons with the orthogous sequence from tobacco chloroplast DNA indicate the direction of change at most of the sites. The results suggest that plastomes I and II are closely related to each other, as are plastomes III and IV. Replication slippage is proposed as a mechanism to explain the length mutations.
A cell-free extract prepared, from X174-infected Escherichia coli cells sustained in vitro synthesis of viral DNA (stage 11 reaction).when supplemented with fraction II from uninfected cells. The reaction was dependent upon deoxyribonucleoside triphosphate,.ATP, added 4X174 replicative form I DNA template, and the fraction II from uninfected cells. This reaction differed from the stage II reaction (semiconservative replication of duplex replicative form DNA) by the production of stable viral protein-DNA complexes sensitive to anti-+X174 antiserum. Three types ofprotein-DNA complexes were identified, '50S, 92S, and a 114S complex that cobanded in CsCl and cosedimented in neutral sucrose gradients with a 4X174 phage marker. The sensitivity of these complexes to anti-4X174.antiserum and Staphylococcus aureus provided a relatively rapid biochemical assay for direct measurement of the amount of DNA synthesized by -the stage m reaction. With this assay, an E. coli factor .(SI,,) required specifically for the synthesis of viral protein-DNA complexes was identified and purified 200-fold from uninfected E. coli cells.' The partially purified Sm factor was required for the synthesis ofDNA and viral protein-DNA complexes in the +X174-infected cell extracts and could not be replaced by rep The publication costs ofthis article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.
Abstract. Oenothera plants grown as shoot meristem cultures on media having a low calcium concentration had a reduced abundance of raphides when compared to greenhouse‐grown plants or shoot meristem cultures grown on higher concentrations of calcium. Plants from the low‐calcium media also yielded a higher proportion of intact chloroplasts during subcellular fractionation.
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