The cyanelle genome of Cyanophora paradoxa, unlike the chloroplast genome, codes for the ribosomal L3 protein.

We describe a 1132 bp sequence of the cyanelle genome of Cyanophora paradoxa containing the rpl3 gene. This gene, which is not chloroplast encoded in plants, is the first of a long cyanelle ribosomal operon whose organization resembles that of the S10 operon of E. coli. We have shown that the rpl3 gene is transcribed in cyanelles as a 7500 nucleotide precursor and that the 5'-end of the mRNA starts approximately 90 nucleotides upstream from the initiation codon. However, no typical procaryotic promoter could be found for this gene. We have detected, using anti E. coli L3 antibodies, the cyanelle L3 protein in cyanelle extracts and in E. coli cells transformed with the cyanelle rpl3 gene.     

A 2.6 kb intron separates the signal peptide coding sequence of an anther-specific protein from the rest of the gene in sunflower

Summary Metabolism of sulfonylurea herbicides by Streptomyces griseolus ATCC 11796 is carried out via two cytochromes P-450, P-450_SU1 and P-450_SU2. Mutants of S. griseolus, selected by their reduced ability to metabolize a fluorescent sulfonylurea, do not synthesize cytochrome P-450_SU1 when grown in the presence of sulfonylureas. Genetic evidence indicated that this phenotype was the result of a deletion of > 15 kb of DNA, including the structural genes for cytochrome P-450_SU1 and an associated ferredoxin Fd-1 (suaC and suaB, respectively). In the absence of this monooxygenase system, the mutants described here respond to the presence of sulfonylureas or phenobarbital in the growth medium with the expression of only the suhC,B gene products (cytochrome P-450_SU2 and Fd-2), previously observed only as minor components in wild-type cells treated with sulfonylurea. These strains have enabled an analysis of sulfonylurea metabolism mediated by cytochrome P-450_SU2 in the absence of P-450_SU1, yielding an in vivo delineation of the roles of the two different cytochrome P-450 systems in herbicide metabolism by S. griseolus.     

Anther-specific,developmentally regulated expression of genes encoding a new class of proline-rich proteins in sunflower

We have used RNA gel blot analysis to demonstrate the anther-specific expression of three genes in sunflower. Expression of these genes was first detected shortly before flower opening, which occurs sequentially on the sunflower inflorescence, and continues during pollination. In contrast, these genes are not expressed (or only weakly expressed) in a male-sterile line in which anther development aborts. In situ hybridization experiments showed that these genes are only expressed in the single cell layer of the sunflower anther epidermis. In the case of one of these genes, which codes for an abundant mRNA, we report the peptide sequences deduced from the sequence of two similar but non identical cDNAs. These proteins contain a potential signal peptide and are characterized by the presence of a proline-rich region which reads KPSTPAPPPPPP(PP)K. Our results also suggest that several proline-rich proteins of unknown functions are specifically synthesized during the maturation of anthers in sunflower.     

The pollen-specific LIM protein PLIM-1 from sunflower binds nucleic acids in vitro

The protein PLIM-1 (formerly SF3) from sunflower is expressed exclusively in mature, free pollen. It contains two LIM domains associated with an acidic C-terminus comprising six copies of the pentapeptide motif (A,T,S) (E,D) TQN. We have expressed the pollen protein as well as some of its mutant forms inEscherichia coli and have used the bacterially produced proteins to study interactions with nucleic acids. Our studies show that the protein binds DNA and RNA in vitro to form large complexes, while mutant polypeptides containing either a single LIM domain or a destabilized first or second LIM domain do not. Although these data suggest that the biological function of PLIM-1 involves interactions with nucleic acids, its role in pollen development remains unclear.     

Effects of low-chloride solutions on action potentials of sheep cadiac purkinje fibers

The rapid repolarization during phase 1 of the action potential of sheep cardiac purkinje fibers has been attributed to a time- and voltage-dependent chloride current. In part, this conclusion was based on experiments that showed a substantial slowing of phase 1 when larger, presumably impermeant, anions were substituted for chloride in tyrode’s solution. We have re- examined the electrical effects of low-chloride solutions. We recorded action potentials of sheep cardiac purkinje fibers in normal tyrode’s solution and in low-chloride solutions made by substituting sodium propionate, acetylglycinate, methylsulfate, or methanesulfonate for the NaCl of Tyrode’s solution. Total calcium was adjusted to keep calcium ion activity of test solutions equal to that of control solutions. Propionate gave qualitatively variable results in preliminary experiments; it was not tested further. Low-chloride solutions made with the other anions gave much more consistent results: phase 1 and the notch that often occurs between phases 1 and 2 were usually unaffected, and the action potential duration usually increased. The only apparent change in the resting potential was a transient 3-6 mV depolarization when low-chloride solution was first admitted to the chamber, and a symmetrical transient hyperpolarization when chloride was returned to normal. If a time- and voltage-dependent chloride current exists in sheep cardiac purkinje fibers, our results suggest that it plays little role in generating phase 1 of the action potential.