Characterization of a gene common to cyanobacteria and higher plants ( psbH) and its possible function in photoinhibition
Abstract
The psbH gene of the photosynthetic cyanobacterium, Synechocystis 6803, has been cloned from a $\lambda$ EMBL 3 library of cyanobacterial chromosomal DNA. The gene is a single copy gene located on a 6.7 kb EcoRI fragment of the chromosomal DNA of Synechocystis 6803. Southern blot analysis and restriction mapping of the 6.7 kb fragment showed that an 0.8 kb fragment contains the coding sequence of the gene. DNA sequence analysis of this 0.8 kb fragment revealed a 70% sequence similarity to the corn psbH gene which was used as a probe. Computer analysis of this sequence revealed an open reading frame of 64 amino acids which had 64% sequence similarity to the corn psbH open reading frame. The phosphorylation site in the higher plant protein is known to be at the threonine residue at the third position in corn. The analogous Synechocystis 6803 gene is missing the first 12 amino acids from the N terminus corresponding to the corn protein, suggesting that the protein is not phosphorylated in Synechocystis 6803. An insertion mutation was created in the psbH gene of the Synechocystis 6803 by inserting a kanamycin resistance gene at the +21 base from the start codon. Photoinhibition studies showed that the presence of 30 mM sodium ascorbate during photoinhibition did not protect against photoinhibition, although 80% of the ascorbate added was in the reduced form after the photoinhibition. The light induced conversion of violaxanthin to zeaxanthin did not affect the thylakoid protein kinase activity. Both the treated sample (which had 7.8 mol zeaxanthin/100 mol chlorophyll a) and the control showed the same extent of phosphorylation. The presence of zeaxanthin during photoinhibition did not protect thylakoids against the photoinhibitory damage. The extent of photoinhibitory damage was similar in both the treatment which has light induced zeaxanthin formation (+Z) and the control ($-$Z). (Abstract shortened with permission of author.)
Degree
Ph.D.
Advisors
Dilley, Purdue University.
Subject Area
Molecular biology
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