Plasmids in two cyanobacterial strains

DNA sequence and analysis of a cryptic 4.2-kb plasmid from the filamentous cyanobacterium, Plectonema sp. strain PCC 6402

The 4194-bp plasmid, pRF1, from Plectonema sp. Strain PCC 6402 was completely sequenced and analyzed. Seven potential open reading frames were identified. The predicted amino acid sequence of open reading frame C (ORF C) had identities of 34, 29, and 25% with Rep B from the Staphylococcus aureus plasmid, pUB110; Rep from the Bacillus amyloliquefaciens plasmid, pFTB14; and protein A from the S. aureus plasmid, pC194, respectively. A 75-amino-acid region conserved in these proteins (Rep B, Rep, and protein A) also was highly conserved in ORF C with identities of 45, 37, and 40%, respectively. Significantly, 16 of the 21 amino acids conserved in Rep B, Rep, and protein A were found at the same positions in ORF C. This ORF may encode a replication protein that includes a region conserved in some eubacteria. Additional structural features include a 425-bp region that contains palindromes, tandem repeats, and short direct repeats which may correspond to the origin of replication. An 18-bp inverted repeat was located between two open reading frames, A and G.

Controlled gene expression utilising lambda phage regulatory signals in a cyanobacterium host

This study presents plasmid systems that utilize regulatory signals of bacteriophage Lambda to accomplish regulated expression of cloned genes in an A. nidulans R2 derivative strain. An operator-promoter region and the temperature-sensitive repressor gene cI857 of bacteriophage Lambda were employed. Linked to a cyanobacterial replicon, the plasmid vectors efficiently transformed Anacystis and were stably maintained within this host. The cat structural gene, encoding chloramphenicol acetyltransferase, was used to demonstrate that expression can be regulated by temperature shift. We have identified in extracts from the vector bearing Anacystis, a protein similar in size and immunology to the Lambda repressor. The systems described should allow controlled expression of adventitious genes in the cyanobacterial host.

A new hybrid plasmid capable of transforming Escherichia coli and Anacystis nidulans

We have constructed a hybrid plasmid, pDF30, by combining the 8-kb pDF3 plasmid derived from the cyanobacterium Anacystis nidulans 6311 with the Escherichia coli vector pBR325. pDF30 transforms, replicates and confers chloramphenicol resistance (Cmr) and ampicillin resistance (Apr) on both A. nidulans and E. coli. The level of resistance to ampicillin in A. nidulans transformants, although low, is above background resistance and an Apr activity was demonstrated in cell-free extracts of A. nidulans that harbored pDF30. pDF30 is stably maintained within E. coli and can be isolated intact from A. nidulans after several months of subculture under chloramphenicol selection and by this criterion is stable in vivo. The unique restriction sites for XhoI, SalI and EcoRI can be used for molecular cloning of chromosomal genes in E. coli and A. nidulans. Until now pDF3 is phenotypically cryptic in both A. nidulans and E. coli. Examination of the polypeptides encoded on and expressed by pDF30 in E. coli minicells revealed only gene products from pBR325 but none from pDF3.