Biology subjects

Stappert, N.

Publications and source records attributed to Stappert, N..

2 recordsLinked to original sources

bioRxiv2026

The relevance of GGCC methylation for cyanobacterial gene expression regulation

Epigenetic DNA modifications are pivotal in eukaryotic gene expression, but their regulatory significance in bacteria is less understood. In the Synechocystis 6803 genome, the DNA-specific methyltransferase M.Ssp6803II modifies the first cytosine in the 38,512 GGCC motifs, forming N4-methylcytosine (GGm4CC). Previous analyses showed that deletion of the gene encoding M.Ssp6803II ({triangleup}sll0729), caused a bluish phenotype due to reduced expression of the hemJ gene. This effect was caused by the lacking GGCC methylation in the discriminator sequence of the hemJ promoter in {triangleup}sll0729. In the present study, we analyzed the impact of GGm4CC methylation on the overall gene expression. Bioinformatic analyses of multiple, independently obtained DNA microarray datasets revealed reproducible changes in the expression of more than 300 genes. We selected 26 genes that had the GGCC methylation motif in different locations of their promoter sequences and verified their differential expression through qPCR experiments. Classification of the promoters according to the relative position of GGCC motifs suggested context-specific effects on gene expression. These findings imply that GGm4CC methylation via DNA methyltransferase M.Ssp6803II has an important impact on proper gene expression and thus, cytosine N4-methylation is a relevant epigenetic marker in Synechocystis and likely many other bacteria.

microbiology↗

bioRxiv2024

Epigenetic control of tetrapyrrole biosynthesis by m4C DNA methylation in a cyanobacterium

Epigenetic DNA modifications are pivotal in eukaryotic gene expression, but their regulatory significance in bacteria is less understood. In Synechocystis 6803, the DNA methyltransferase M.Ssp6803II modifies the first cytosine in the GGCC motif, forming N4-methylcytosine (GGm4CC). Deleting the sll0729 gene ({Delta}sll0729) caused a bluish phenotype due to reduced chlorophyll levels, which was reversed by suppressor mutations. Re-sequencing of seven suppressor clones revealed a common GGCC to GGTC mutation in the slr1790 promoters discriminator sequence, encoding protoporphyrinogen IX oxidase, HemJ, crucial for tetrapyrrole biosynthesis. Transcriptomic and qPCR analyses indicated aberrant slr1790 expression in {Delta}sll0729 mutants. This aberration led to the accumulation of coproporphyrin III and protoporphyrin IX, indicative of impaired HemJ activity. To confirm the importance of DNA methylation in hemJ expression, native and mutated hemJ promoter variants were introduced into the wild type, followed by sll0729 deletion. The sll0729 deletion segregated in strains with the GGTC motif in the hemJ promoter, resulting in wild-type-like pigmentation, whereas freshly prepared {Delta}sll0729 mutants with the native hemJ promoter exhibited the bluish phenotype. These findings demonstrate that hemJ is tightly regulated in Synechocystis and that N4-methylcytosine is essential for proper hemJ expression.

microbiology↗