Structure and expression of three light-harvesting chlorophyll a/b-binding protein genes in Arabidopsis thaliana.

The genome of Arabidopsis thaliana is exceedingly small, in part because it lacks the large middle repetitive DNA component characteristic of other plants. In this paper we have characterized a member of the low copy DNA component: the gene family for the light-harvesting chlorophyll a/b-protein. This gene family is unusual in that it contains far fewer members than the 7-16 coding sequences for this protein found in other plants. We used cross-hybridization with a Lemna gene encoding a light-harvesting chlorophyll a/b-protein to isolate 3 genes from Arabidopsis, all of which are clustered on an 11-kb genomic clone. Southern blot analysis suggests that there is a fourth related gene in Arabidopsis. Sequence analysis of the three genes demonstrates that within the translated region the nucleic acid sequence homology is 96%, the deduced amino acid sequence of the mature proteins is identical for the three genes, and two of the genes have a high degree of sequence homology in both their 5' and 3' immediate flanking regions. The genes have regulatory sequences typical of eukaryotic genes upstream of the translation start sites. However, not all of these genes are equally expressed in plants grown under normal light-dark conditions.

Absence of significant light-induced changes in cAMP levels in sporangiophores of Phycomyces blakesleeanus.

We were unable to find transient changes in the amount of cAMP or cGMP that had been proposed to mediate the light-growth response in sporangiophores of Phycomyces blakesleeanus.

Biosynthesis of aryl carotenoids: inhibitor studies of chlorobactene biosynthesis in Chlorobium limicola f. thiosulfatophilum.

The biosynthesis of the aryl carotenoid, chlorobactene, was examined in the green sulfur bacterium, Chlorobium limicola f. thiosulfatophilum. Nicotine, which was used to inhibit carotenoid cyclization, caused the accumulation of the acyclic carotenoid, lycopene. Cells reincubated in fresh medium, after removal of nicotine, synthesized chlorobactene more readily from newly synthesized lycopene rather than from the pool of lycopene accumulated during nicotine inhibition. When the cells were reincubated in the presence of diphenylamine, which inhibited de novo carotenogenesis, a portion of the lycopene which had accumulated during nicotine inhibition was converted into chlorobactene. There was no evidence that neurosporene, rather than lycopene, was the precyclization intermediate. The involvement of gamma-carotene as the cyclic precursor of chlorobactene also was shown. The pathway for chlorobactene biosynthesis is discussed in terms of a possible arrangement of the enzymes involved in carotenoid biosynthesis.