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D C Youvan

Publications and source records attributed to D C Youvan.

46 records · Page 3Linked to original sources
PubMed1985

Light-harvesting II (B800-B850 complex) structural genes from Rhodopseudomonas capsulata.

The light-harvesting II (LHII) structural genes coding for the (B800-B850 complex) beta- and alpha-polypeptides have been cloned and the nucleotide and deduced polypeptide sequences have been determined. This completes the sequencing of all seven structural genes coding for the structural polypeptides of the photosynthetic apparatus that bind the pigments and cofactors participating in the primary light reactions of photosynthesis. Unlike the structural genes coding for the reaction center L, M, and H subunits and the light-harvesting I (LHI) (B870 complex) structural polypeptides, the LHII structural genes are not within the 46-kilobase photosynthetic gene cluster carried by the R-prime plasmid pRPS404. Identical organization of the beta and alpha structural genes for both LHI and LHII and sequence homologies between the two beta-polypeptides and between the two alpha-polypeptides suggests that both complexes arose by gene duplication from a single ancestral light-harvesting complex and that the putative bacteriochlorophyll binding sequence Ala-X-X-X-His has been absolutely conserved.

Journal Article↗
PubMed1984

Nucleotide and deduced polypeptide sequences of the photosynthetic reaction-center, B870 antenna, and flanking polypeptides from R. capsulata.

The complete nucleotide sequence (8867 bp) and the deduced polypeptide sequence are given for 11 proteins from the photosynthetic gene cluster of R. capsulata (46 kb), including the photosynthetic reaction-center L, M, and H subunits and the B870 alpha and B870 beta polypeptides (light-harvesting I). These polypeptides bind bacteriochlorophyll, bacteriopheophytin, carotenoids, and quinones that are involved in the primary light reactions of photosynthesis. Hydropathy plots indicate that the L and M subunits are transmembrane proteins that may cross the membrane five times, while the H subunit has only one hydrophobic section near the amino terminus, which may be transmembrane. The L and M subunits are homologous over their entire length and have a high degree of homology with the QB protein from photosystem II of higher plants. An additional six genes were identified that may have some unknown role in bioenergetics since only mutations that affect the differentiation of the photosynthetic apparatus are known to map to this gene cluster.

Amino Acid Sequence↗
PubMed1984

Reaction center and light-harvesting I genes from Rhodopseudomonas capsulata.

Five structural genes coding for the reaction center (RC) L, M, and H subunits and the two light-harvesting (LH) I polypeptides, B870alpha and B870beta, have been mapped on two restriction fragments from the R-prime plasmid pRPS404. It has been recently shown that enhanced near-infrared fluorescence mutants of Rhodopseudomonas capsulata typically lack RC or LH I polypeptides and that these lesions are marker-rescued by two restriction fragments from the R-prime plasmid: the 7.5-kilobase-pair EcoRI F fragment and the 4.75-kilobase-pair BamHI C-EcoRI fragment. We have now determined the nucleotide sequence of two restriction fragments and have found that the BamHI C-EcoRI B fragment carries the structural genes for the RC L and M subunits and both LH I polypeptides. Forty kilobase pairs away from this locus, the BamHI F fragment (within the EcoRI F fragment) carries the RC H subunit. The structural genes on the BamHI C-EcoRI B fragment are probably transcribed as part of a polycistronic mRNA. All of the structural genes begin with a consensus Shine-Dalgarno sequence and separate AUG start codons, indicating that the structural polypeptides are not cleaved from larger precursor polypeptides.

Journal Article↗
PubMed1983

Isolation and characterization of enhanced fluorescence mutants of Rhodopseudomonas capsulata.

After enrichment by a tetracycline suicide under conditions nonpermissive for the growth of mutants defective in photosynthesis, colonies were screened for enhanced fluorescence in near-infrared light by using high-speed infrared photography. Twenty mutants were isolated, and the chromatophore membranes were analyzed by a new, rapid microprocedure that revealed many different phenotypes among the mutants. The enhanced fluorescence mutants typically possessed a functional light-harvesting II antenna, but showed reduced or absent light-harvesting I. Twelve isolates were also defective in reaction center polypeptides. An R-prime plasmid that bears 50 kilobases of Rhodopseudomonas capsulata DNA coding for components of the photosynthetic apparatus (B. L. Marrs, J. Bacteriol. 146:1003-1012, 1981), pRPS404, complemented all 20 enhanced fluorescence mutants as demonstrated by the quenching of fluorescence in mutants that had received the R-prime plasmid by conjugation. Fluorescence was regained upon loss of the 50-kilobase insert. Complementation of the fluorescent lesions implies that most or all of the genes necessary for the expression of the reaction center and the light-harvesting antennae are carried by the R-prime plasmid and that these genes are actively transcribed in the homologous organism. All 20 mutants are complemented by one of two pBR322 subclones of the R-prime plasmid, pRPSEB2 or pRPSE2. pRPSEB2 bears a 4.5-kilobase fragment of R. capsulata DNA including the rxcA locus, and pRPSE2 is a pBR322 derivative bearing a 7.5-kilobase R. capsulata DNA fragment bearing the rxcB locus. These fragments therefore carry sequences necessary for the normal synthesis of the light-harvesting and reaction center polypeptide complexes.

Bacterial Proteins↗
PubMed1981

A sequence from Drosophila melanogaster 18S rRNA bearing the conserved hypermodified nucleoside am psi: analysis by reverse transcription and high-performance liquid chromatography.

The naturally occurring modified nucleoside 3-[3-amino-3-carboxypropyl]-1-methylpseudouridine (abbreviated am psi) is found in eukaryotic 18S rRNA. We localized am psi to sequence resolution in D. melanogaster 18S rRNA. This hypermodified base causes an absolute stop in cDNA elongation. The RNA sequence bearing am psi was determined by dideoxy-sequencing with reverse transcriptase. The rDNA coding for this part of the 18S rRNA was sequenced by the Maxam-Gilbert method. Together these two sequencing methods can be used to position the cDNA stop (am psi) in the rRNA sequence. Chemical evidence for the existence of am psi in this RNA sequence was obtained by high-performance liquid chromatography (HPLC) of 18S rRNA nucleosides from radioactive-labeled cells. L-[2-14C] methionine will selectively label am psi in eukaryotic 18S rRNA. Using HPLC, we found a single 14C-labeled nucleotide in digests of 18S rRNA. This nucleotide is in the RNA sequence bearing the cDNA stop since a restriction fragment which hybridizes to this sequence protects the modified base from RNase T1 digestion.

Animals↗
PubMed1979

Reverse transcriptase pauses at N2-methylguanine during in vitro transcription of Escherichia coli 16S ribosomal RNA.

A restriction fragment strand complementary to a sequence near the 3' end of Escherichia coli 16S rRNA has been used to prime reverse transcriptase (avian myeloblastosis virus RNA-directed DNA nucleotidyltransferase; deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7). In addition to transcripts that were extended to the 5' end of the RNA, two major transcription intermediates were observed. These discrete-sized cDNA intermediates are the result of a kinetic barrier imposed by monomethylation of the amino group on guanine that participates in base-pairing. Both major transcription intermediates correspond to attenuation at the known positions of N2-methylguanine (m2G) in the rRNA sequence. The relaxation time for elongation of the cDNA through m2G is approximately 3 min. No other major kinetic pauses were observed in the 1340 bases transcribed.

Base Sequence↗
PubMed1978

Structure of psoralen-crosslinked ribosomal RNA from Drosophila melanogaster.

Ribosomal RNA from Drosophila melanogaster photoreacted with hydroxymethyltrioxsalen has been examined by electron microscopy. Reproducible patterns of hairpins were found in both the 26S and 18S RNA. The frequency of these hairpins and the amount of incorporated drug were dependent upon the conditions under which the crosslinking was performed. A prominent central hairpin occurs in the 26S RNA and the break that interrupts the continuity of the RNA chain is located within it. In addition to several small hairpins, the crosslinked 18S RNA contains a large open loop.

Animals↗