Tandem sequence duplications functionally complement deletions in the D1 protein of photosystem II

H. Kless, Willem Vermaas

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13 Scopus citations

Abstract

Obligate photoheterotrophic mutants of the cyanobacterium Synechocystis sp. PCC 6803 that carry deletions of conserved residues in the plastoquinone- binding niche of the D1 protein were used to select for spontaneous mutations that restore photoautotrophic growth. Spontaneous pseudorevertants emerged from two deletion mutants, ΔYNIV246-9 and ΔNN266-7, when the cultures were maintained long after the carbon source (glucose) had been depleted from the medium and cells had reached stationary phase. Most pseudorevertants were found to contain tandem duplications of 6-45-base pair DNA sequences located close to the domain carrying the deletion; none of them restored the wild-type sequence. Three pseudorevertants isolated from the ΔYNIV246-9 mutant contained a duplication (7-15 codons) of the DNA sequence immediately downstream of the deletion; the protein region encoded by this DNA may include part of the putative de helix, an important constituent of the plastoquinone-binding niche. Three pseudorevertants isolated from the ΔNN266-7 mutant contained duplications corresponding to 2-8 amino acid residues adjacent to the site of the deletion. In all six pseudorevertants carrying duplications, the length of the D1 protein in the modified regions was restored to at least the length present in wild type, suggesting that a minimal length of these protein domains may be required for functional integrity. In another photoautotrophic strain isolated from ΔNN266-7, secondary mutations could be identified in the gene coding for the D1 protein; such mutations apparently reside on another protein subunit of the photosystem II complex. Photosystem II function in the pseudorevertants was altered as compared with wild type in terms of growth and oxygen evolution rates, photosystem II concentration, the semiquinone equilibrium at the acceptor side, and thermostability. A mechanism leading to tandem sequence duplication may involve DNA damage followed by DNA synthesis, strand displacement, and ligation.

Original languageEnglish (US)
Pages (from-to)16536-16541
Number of pages6
JournalJournal of Biological Chemistry
Volume270
Issue number28
DOIs
StatePublished - 1995

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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