Open AccessIdentification and characterization of hetA, a gene that acts early in the process of morphological differentiation of heterocysts
Author(s) -
D.B. Holland,
C. Peter Wölk
Publication year - 1990
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.172.6.3131-3137.1990
Subject(s) - biology , open reading frame , genetics , gene , mutant , nucleic acid sequence , complementation , microbiology and biotechnology , sequence analysis , direct repeat , heterocyst , peptide sequence , structural gene , anabaena , cyanobacteria , bacteria , base sequence
Envelope polysaccharide is a major early diagnostic of differentiating heterocysts. The mutation in mutant EF116 of Anabaena sp. strain PCC 7120 reduces the cohesiveness of this polysaccharide. A 3.5-kilobase fragment of DNA cloned from the wild type of this Anabaena sp. was previously shown to complement this mutation. We present the nucleotide sequence of a 2,555-base-pair portion of this fragment containing an open reading frame (ORF) of 601 amino acids. Complementation analysis using deletion derivatives of the 3.5-kilobase fragment showed that the gene mutated in EF116, which we designate hetA, lies within this ORF. Transcription of hetA was induced as a result of deprivation for nitrate and yielded a monocistronic mRNA that was present at greatest abundance 7 h after nitrogen stepdown. At that time, proheterocysts could not be distinguished by light microscopy; transcription of nifHD, structural genes of nitrogenase, peaked much later. Situated 3' to hetA are 4 identical repeats of the sequence 5'-TTCAAAA-3' and 12 repeats (10 identical) of the sequence 5'-CCCCAAT-3'. The 12 repeats, present within and near the 5' end of a second ORF, are almost identical to repeats that have been reported to be present in the region between the petC and petA genes of a related cyanobacterium.