An extracellular protease of Staphylococcus aureus, strain V8, previously shown to cleave specifically the peptide bonds on the carboxyl-terminal side of either aspartate or glutamate residues in phosphate buffer (pH 7.8) hydrolyzes only glutamoyl bonds in either ammonium bicarbonate (pH 7.8) or ammonium acetate (pH 4.0). Of all aspartoyl bonds tested, only the Asp-Gly linkage is cleaved at a detectable rate. The staphylococcal protease hydrolyzes all of the seventeen different glutamoyl bonds studied, although those involving hydrophobic aminoacid residues with bulky side chains are cleaved at a lower rate.-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~T he purification of a proteolytic enzyme from the culture filtrates of Staphylococcus aureus, strain V8, has recently been reported (1). Partial characterization of this protease indicated that it had a molecular weight of 12,000, was inhibited by diisopropyl fluorophosphate, and was active over the pH range of 3.5-9.5, but exhibited maximal activity at pH 4.0 and 7.8 with hemoglobin as substrate. Digestion of oxidized ribonuclease by' the protease, followed by identification of the amino-and carboxyl-terminal residues of the liberated peptides, revealed that the protease cleaved specifically peptide bonds on the carboxyl-terminal side of either aspartic acid or glutamic acid. The specificity of the protease for bonds involving only dicarboxylic amino acids was also demonstrated by the inability of the enzyme to degrade casein in which all of its carboxyl groups had been coupled with glycine ethyl ester in amide linkage, whereas unmodified casein was readily digested.At pH 7.8, in sodium or potassium phosphate buffer, both aspartoyl and glutamoyl peptide bonds were cleaved (1). 2,3; 9,10; 49,50; 86,87; and 111,112. Apparently, none of the five aspartoyl bonds also present in ribonuclease had been hydrolyzed.

Prochlorococcus marinus. The purification and properties of the axenic strain PCC 9511, derived from the same primary culture (SARG) as the type species, are reported here. Prochlorococcus PCC 9511 differs from the latter in possessing horseshoeshaped thylakoids, exhibiting a low chlorophyll b 2 content and lacking phycoerythrin, but shares these phenotypic properties with Prochlorococcus strain CCMP 1378. This relationship was confirmed by 16S rRNA sequence analyses, which clearly demonstrated that the axenic isolate is not co-identic with the nomenclatural type. Strain PCC 9511 has a low mean DNA base composition (32 mol % GMC) and harbours the smallest genome of all known oxyphotobacteria (genome complexity 13 GDa l 2 Mbp). Urea and ammonia are the preferred sources of nitrogen for growth, whereas nitrate is not utilized. Several different organic phosphorus compounds efficiently replace phosphate in the culture medium, indicative of ecto-phosphohydrolase activity. In order to distinguish strain PCC 9511 from the nomenclatural type, a new subspecies is proposed, Prochlorococcus marinus Chisholm et al. 1992 subsp. pastoris subsp. nov. This paper is dedicated in gratitude to Professor Germaine Cohen-Bazire on the occasion of her 80th birthday. Together with her late husband, Professor R. Y. Stanier, Germaine gave the members of the Physiologie Microbienne (Institute Pasteur, Paris) generous scientific guidance and spiritual support over many years (1971)(1972)(1973)(1974)(1975)(1976)(1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988) Abbreviations : chl, chlorophyll ; HL, high light ; LL, low light ; PPFD, photosynthetic photon flux density ; PE, phycoerythrin ; T m , temperature mid-point of denaturation. Keywords :The GenBank accession numbers for the 16S rRNA sequences of PCC 9511, CCMP 1426 and NATL1 are AF180967, AF133833 and AF133834, respectively. INTRODUCTIONIn the last edition of Bergey's Manual of Systematic Bacteriology, the class Oxyphotobacteria was subdivided into the Cyanobacteria, whose ordinal recognition still awaits validation, and the order Prochlorales Lewin 1977(Castenholz & Waterbury, 1989. In the light, like algae and plants, these photosynthetic prokaryotes use H # O for the generation of chemical energy and reducing power and liberate molecular O # as a by-product. The demand for cellular carbon is met by CO # fixation. Cyanobacteria synthesize monovinyl chlorophyll a (chl a " ) and harvest light by aid of watersoluble multimeric complexes, the phycobilisomes, composed of biliproteins and linker polypeptides R. Rippka and others (Glazer, 1987(Glazer, , 1989Sidler, 1994). In contrast, oxyphotobacteria of the order Prochlorales Lewin 1977 either lack phycobiliproteins entirely, or synthesize only trace amounts (Lewin, 1977(Lewin, , 1989 BurgerWiersma et al., 1986 ;Chisholm et al., 1992 ;Hess et al., 1996). Their light-harvesting complexes are membrane-associated proteins containing chlorophyll a (a " or a # ) and chlorophyll b (b " or b # ) as the major photosyntheti...

Dating from the Pre‐Cambrian era, cyanobacteria have a long history of adaptation to the Earth's environment. By evolving oxygen via photosynthetic reactions similar to those of plants and green algae, these prokaryotes were essential to the evolution of the present biosphere. They continue to make a large contribution to the equilibrium of the Earth's atmosphere by production oxygen and removing carbon dioxide. To survive in extreme or variable environments, cyanobacteria have developed specific regulatory systems, in addition to more general mechanisms equivalent to those of other prokaryotes or photosynthesis eukaryotes. Specific regulatory systems control the differentiation of specialized nitrogen‐fixing cells and of cell types facilitating the dispersion of species. In the past decade, considerable progress has been made towards understanding the expression of the cyanobacterial genome in response to variations in the intensity and spectral quality of incident light and in response to nutritional conditions, especially carbon, nitrogen and sulphur sources. These studies have provided insights into the relationships between carbon and nitrogen intermediary metabolism, and a start towards understanding of the interconnected pathways which lead from the perception of environmental signals to the regulation of enzyme activities and gene expression. Cyanobacterial regulatory mechanisms share common features with those of other prokaryotes, but are unique since these essentially photo‐autotrophic organisms must maintain a proper cellular C/N balance, in spite of dailty variations in incident light. Thus an appropriate coordination between photosynthesis and other metabolic processes must be achieved through control of the catalytic activity of key enzymes by reducing equivalents and ATP produced by photosynthetic or respiratory electron transport. Recently discovered kinases/phosphatases act by post‐translational modification of specific proteins which probably act as signal transducers or modulators of gene expression in a manner similar to the well‐known two‐component regulatory systems described in other bacteria. In this overview, we present our current knowledge on the molecular aspects of the biology of cyanobacteria, as well as on their mechanisms of resistance to metal ions and their responses to metabolic stress.

Phycobilisomes, the major light-harvesting complexes of cyanobacteria are multimolecular structures made up of chromophoric proteins called phycobiliproteins and non chromophoric linker polypeptides. We report here the isolation and nucleotide sequence of the genes, cpeA and cpeB, which in Calothrix PCC 7601 encode the alpha and beta subunits of phycoerythrin, one of the major phycobiliproteins. In Calothrix PCC 7601, modulation of the polypeptide composition of the phycobilisomes occurs in response to changes of the light wavelength, a phenomenon known as complementary chromatic adaptation. Under green illumination, cells synthesize phycoerythrin and its two specifically associated linker polypeptides (LR35 and LR36), while under red illumination none of these proteins are detected. Using specific probes, a single transcript (1450 nucleotide long) corresponding to the cpe genes was detected but only in green-light-grown cells, establishing the occurrence of transcriptional regulation for the expression of this operon in response to light wavelength changes. The size of this transcript excludes the possibility that the phycoerythrin-associated LR35 and LR36 could be cotranscribed with the cpeA and cpeB genes.