Replacement of the invariant lysine 77 by arginine in yeast iso-1-cytochrome c results in enhanced and normal activities in vitro and in vivo

Oligonucleotide-directed mutagenesis of the yeast Saccharomyces cerevisiae was used to generate an abnormal iso-1-cytochrome c having an Arg-77 replacement of the normal Lys-77; this Lys-77 residue is evolutionarily conserved in most eukaryotic cytochromes c and is trimethylated in fungal and plant cytochromes c. Examination of strains having a single chromosomal copy of the gene encoding the Arg-77 protein indicated that the altered protein was synthesized at the normal rate and that it had normal or near normal activity in vivo. Examination of enzymatic activities in vitro with cytochrome b2, cytochrome c peroxidase, and cytochrome c oxidase indicated that the altered iso-1-cytochrome c has equal or enhanced catalytic efficiencies. Thus, replacement of the evolutionarily conserved residue Lys-77 produces no or only minor effects both in vivo and in vitro.     

Enzyme-coding genes as molecular clocks: The molecular evolution of animal alpha-amylases

Summary We constructed a cDNA library for the beetle,Tribolium castaneum. This library was screened using a cloned amylase gene fromDrosophila melanogaster as a molecular probe. Beetle amylase cDNA clones were isolated from this bank, and the nucleotide sequence was obtained for a cDNA clone with a coding capacity for 228 amino acids. Both the nucleotide sequence and predicted amino acid sequence were compared to our recent results forD. melanogaster alpha-amylases, along with published sequences for other alpha-amylases. The results show that animal alpha-amylases are highly conserved over their entire length. A borader comparison, which includes plant and microbial alpha-amylase sequences, indicates that parts of the gene are conserved between prokaryotes, plants, and animals. We discuss the potential importance of this and other enzyme-coding genes for the construction of molecular phylogenies and for the study of the general question of molecular clocks in evolution.     

Expression of surface antigen and mRNA for the CD11c (alpha X, p150) subunit of the human leukocyte adherence receptor family in hematopoietic cells

We characterized the surface antigen and mRNA expression for the CD11c (alpha X, p150) subunit of the human leukocyte adherence receptor family during hematopoietic cell differentiation. The CD11c subunit antigen and mRNA are constitutively expressed in undifferentiated HL-60 promyelocytic leukemia cells, and levels increase markedly with differentiation along the monocyte/macrophage pathway using phorbol myristate acetate. Human monocyte-derived macrophages and human alveolar macrophages express elevated levels of the CD11c subunit antigen and mRNA, indicating that the changes observed in vitro are present in vivo. Dot blot analysis of immature and mature lymphoid and myeloid cells and cell lines demonstrate equivalent levels of CD11c mRNA expression. We conclude that CD11c gene expression is selectively increased during hematopoietic cell differentiation along the monocyte/macrophage pathway.     

Amylase gene expression in intraspecific and interspecific somatic transformants of Drosophila.

The Amylase locus in Drosophila melanogaster normally contains two copies of the structural gene for alpha-amylase, a centromere-proximal copy, Amy-p, and a distal copy, Amy-d. Products of the two genes may display discrete electrophoretic mobilities, but many strains known to carry the Amy duplication are characterized by a single amylase electromorph, e.g., Oregon-R, which produces the mobility variant AMY-1. A transient expression assay was used in somatic transformation experiments to test the functional status of the Amy genes from an Oregon-R strain. Plasmid constructs containing either the proximal or distal copy were tested in amylase-null hosts. Both genes produced a functional AMY-1 isozyme. Constructs were tested against an AMY-3 reference activity produced by a coinjected plasmid that contains the Amy-d3 allele from a Canton-S strain. With reference to the internal control, the Amy-p and Amy-d genes from Oregon-R expressed different relative activity levels for AMY-1 in transient assays. The transient expression assay was successfully used to test the functional status of Amy-homologous sequences from strains of other species of Drosophila characterized by a single amylase elctromorph, namely, Drosophila pseudoobscura ST and Drosophila miranda S 204. The amylase-null strain of D. melanogaster provided the hosts for these interspecific somatic transformation experiments.     

Regulation of aromatase mRNA and estradiol biosynthesis in rat ovarian granulosa and luteal cells by prolactin

Regulation by PRL of aromatase (P450arom) mRNA and protein and estradiol (E) biosynthesis was examined in granulosa cells during early stages of luteinization in vitro and in vivo. PRL caused a dose-dependent (10-1000 ng/ml) decrease in P450arom mRNA and E biosynthesis (greater than 99%) in luteinized rat granulosa cells in vitro, even when the cells were cultured in the presence of insulin and hydrocortisone (hormones known to synergize with PRL to induce proteins in mammary tissue) or in the presence of forskolin (a nonhormonal stimulator of cAMP). PRL also prevented the marked increases in aromatase mRNA and E biosynthesis stimulated by FSH and forskolin in nonluteinized preovulatory granulosa cells in culture. These effects of PRL on granulosa cells in culture were specific for aromatase and were not observed for other proteins, such as cholesterol side-chain cleavage cytochrome P450 (P450scc) and alpha 2-macroglobulin. PRL also decreased P450arom mRNA and protein during the early stages of luteinization in vivo. PRL administered to rats beginning day 1 postovulation to mimic hormone release during pseudopregnancy reduced the progressive increase in P450arom mRNA occurring in corpora lutea on days 3-4 in ovulated rats not treated with PRL. CB 154, a dopamine agonist that inhibits pituitary release of PRL, caused P450arom mRNA and protein to decrease 50% if given to pregnant rats on days 8-10 of gestation, but increased P450arom mRNA and protein if given to pregnant rats on days 10-12 of gestation. These diverse effects of PRL in pregnancy suggest that placental factors may modify the response of luteal cells to PRL during gestation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Analysis of the Escherichia coli glycogen gene cluster suggests that catabolic enzymes are encoded among the biosynthetic genes

The nucleotide sequences of the Escherichia coli genome between the glycogen biosynthetic genes glgB and glgC, and 1170 bp of DNA which follows glgA have been determined. The region between glgB and glgC contains an open reading frame (ORF) of 1521 bp which we call glgX. This ORF is capable of coding for an M_r 56 684 protein. The deduced amino acid (aa) sequence for the putative product shows significant similarity to the E. coli glycogen branching enzyme, and to several different glucan hydrolases and transferases. The regions of sequence similarity include residues which have been reported to be involved in substrate binding and catalysis by taka-amylase. This suggests that the proposed product may catalyze hydrolysis or glycosyltransferase reactions. The cloned region which follows glgA contains an incomplete ORF (1149 bp), glgY, which appears to encode 383 aa of the N terminus of glycogen phosphorylase, based upon sequence similarity with the enzyme from rabbit muscle (47% identical aa residues) and with maltodextrin phosphorylase from E. coli (37% identical aa residues). Results suggest that neither ORF is required for glycogen biosynthesis. The localization of glycogen biosynthetic and degradative genes together in a cluster may facilitate the regulation of these systems in vivo.     

Evolutionary conservation of the chromosomal configuration and regulation of amylase genes among eight species of the Drosophila melanogaster species subgroup

Nuclear DNA was extracted from each of the eight species comprising the Drosophila melanogaster species subgroup. Southern hybridization of this DNA by using a molecular probe specific for the alpha-amylase coding region showed that the duplicated structure of the amylase locus, first found in D. melanogaster, is conserved among all species of the melanogaster subgroup. Evidence is also presented for the concerted evolution of the duplicated genes within each species. In addition, it is shown that the glucose repression of amylase gene expression, which has been extensively studied in D. melanogaster, is not confined to this species but occurs in all eight members of the species subgroup. Thus, both the duplicated gene structure and the glucose repression of Drosophila amylase gene activity are stable over extended periods of evolutionary time.      

Phylogenetic evidence for the herbaceous origin of angiosperms

The ancestral angiosperm is commonly interpreted as an arborescent to shrubby magnolialean with large, multiparted, complex flowers. We examined this hypothesis using a phylogenetic analysis of new and reevaluated characters polarizabled with outgroup comparison. Our cladistic analysis of basal angiosperms placed the nonmagnolialeanChloranthaceae andPiperaceae at the bottom of the tree. We further inferred the probable ancestral states of characters not polarizable with outgroup comparison by examining their distribution among taxa at the base of our cladogram. The sum of ancestral character states suggests that the protoangiosperm was a diminutive, rhizomatous to scrambling perennial herb, with small, simple flowers.