Effects of 5-azacytidine on physiological differentiation of Streptomyces antibioticus

The SCO1731 methyltransferase modulates actinorhodin production and morphological differentiation of Streptomyces coelicolor A3(2)

Streptomyces coelicolor is a Gram-positive microorganism often used as a model of physiological and morphological differentiation in streptomycetes, prolific producers of secondary metabolites with important biological activities. In the present study, we analysed Streptomyces coelicolor growth and differentiation in the presence of the hypo-methylating agent 5′-aza-2′-deoxycytidine (5-aza-dC) in order to investigate whether cytosine methylation has a role in differentiation. We found that cytosine demethylation caused a delay in spore germination, aerial mycelium development, sporulation, as well as a massive impairment of actinorhodin production. Thus, we searched for putative DNA methyltransferase genes in the genome and constructed a mutant of the SCO1731 gene. The analysis of the SCO1731::Tn5062 mutant strain demonstrated that inactivation of SCO1731 leads to a strong decrease of cytosine methylation and almost to the same phenotype obtained after 5-aza-dC treatment. Altogether, our data demonstrate that cytosine methylation influences morphological differentiation and actinorhodin production in S. coelicolor and expand our knowledge on this model bacterial system.

DNA rearrangements at the extremities of the Streptomyces ambofaciens linear chromosome: evidence for developmental control

In Streptomyces, a genomic instability results from frequent recombination events which occur at the ends of the linear chromosomal DNA. These events are believed to be responsible for the variability observed in these regions among Streptomyces species and strains. In order to identify functions able to control this type of genome plasticity, mutators as well as mutants produced at different stages of development have been characterized in S. ambofaciens. Their characterization suggests the existence of a relationship between genomic instability and colony development.

Genomic structure of the human DNA methyltransferase gene

We determined the genomic structure of the gene encoding human DNA methyltransferase (DNA MTase). Six overlapping human genomic DNA clones which include all of the known cDNA sequence were isolated. Analysis of these clones demonstrates that the human DNA MTase gene consists of at least 40 exons and 39 introns spanning a distance of 60 kilobases. Elucidation of the chromosomal organization of the human DNA MTase gene provides the template for future structure-function analysis of the properties of mammalian DNA MTase.

Restriction analysis of actinomycetes chromosomal DNA

Actinomycetes DNAs were digested with restriction enzymes to study the presence of methylated bases. Analysis showed that the enterobacterial Dam and Dcm systems are absent. Methylation at the internal cytosine in CCGG sequences, typical of eukaryotes, was also absent. We also tested 18 restriction endonucleases recognizing six base pair sequences (all of which were inhibited by methylation). Results showed a higher number of restriction sites for enzymes recognizing CG-rich sequences (CG endonucleases) than for enzymes recognizing AT-rich sequences (AT endonucleases). Restriction patterns with CG endonucleases were quite uniform, with the remarkable exception of XhoI, which yielded a small number of DNA bands. The study performed with AT endonucleases allowed differentiation of three groups of enzymes based on different degrees of chromosomal sensitivity. One group (BclI and BglII) produced restriction patterns with more abundant restriction sites than expected, a second group (ClaI, EcoRI, and EcoRV) yielded the predicted number of DNA fragments, and the third group (HpaI, HindIII, XbaI, and DraI) produced an unexpectedly low number of fragments. Some individual cases of resistance to particular enzymes could be explained by the presence of restriction-modification systems with the same specificity.