Relationship between Gene Dosage and Gene Expression in the Chloroplast of Chlamydomonas reinhardtii.

Expression of three chloroplast genes encoding proteins of different chloroplast complexes and the rRNA gene has been examined in cells having reduced numbers of chloroplast genomes as a result of growth in the presence of the thymidine analog 5-fluorodeoxyuridine. While accumulation of total mRNA for rpl2 (ribosomal protein L-1), rbcL (ribulose bisphosphate carboxylase large subunit) and atpA (alpha-subunit of ATP synthase) declined with gene copy number, the levels of translatable mRNA and rates of synthesis of these three proteins were largely unaffected. Accumulation of rRNA declined less precipitously than mRNA levels for the three proteins in response to the reduction in chloroplast genome number. Chlamydomonas appears to compensate for reductions in the number of chloroplast genomes at several different levels. Populations of cells with only one-fourth the wild-type amount of chloroplast DNA per cell on average have half the normal level of chloroplast ribosomes and nearly normal rates of CO(2) fixation and levels of specific chloroplast encoded proteins. These results suggest that normal cells accumulate a large excess of transcripts for chloroplast genes and that levels of expression of these genes are regulated by posttranscriptional mechanisms.

Interactions of Escherichia coli and marine bacteria with 241Am in laboratory cultures.

In nutrient media, Escherichia coli and selected strains of marine facultative anaerobes accumulated significant amounts of the transuranic radioisotope 241Am. The pattern of uptake varied among strains and was dependent upon pH, culture media and growth stage of the population. Desorption of 241Am to montmorillonite was significantly less in filtered media from some bacterial cultures than in "unconditioned" control media, suggesting that bacterial exometabolites may form complexes with Am thereby increasing its solubility.

Intraspecific variation in the structural organization and redundancy of chloroplast ribosomal DNA cistrons in Euglena gracilis.

Chloroplast DNAs from six different laboratory collections of Euglena gracilis "strain Z" and var. bacillaris were analyzed with restriction endonucleases EcoRI and Bam HI. The most variable portion of the organelle genome is the region containing the ribosomal cistrons. Intraspecific differences occur in both ribosomal DNA cistron number (one or three) and structural organization among those strains designated as "strain Z" and bacillaris. One culture previously designated as "Z" is most likely bacillaris.

Perturbation of chloroplast DNA amounts and chloroplast gene transmission in Chlamydomonas reinhardtii by 5-fluorodeoxyuridine.

5-Fluorodeoxyuridine selectively decreases the rate of chloroplast DNA replication in Chlamydomonas resulting after several generations of growth in equilibrium levels as low as one-seventh of normal. When the maternal parent is treated prior to mating, the decrease of chloroplast DNA appears to perturb the normal maternal transmission of chloroplast genes, dramatically increasing the proportion of exceptional zygotes transmitting chloroplast genes from the paternal parent.