Gate-Keeping transcription through histone H3 K42, a novel site of methylation in the yeast nucleosome core

A new site of methylation was identified on histone H3 K42 in Saccharomyces cerevisiae. Mutations were engineered at this site to mimic either a constitutively modified state, K42L, or a constitutively unmodified state, K42Q in addition to an alanine substitution. K42A. The effects of these mutations on global transcription was monitored in yeast cells whose sole source of histone H3 was from a plasmid expressing these mutant proteins, and compared to that of an isogenic strain expressing the wild-type histone H3 protein from the same plasmid. Two biological replicates are included for each yeast strains expressing a specific histone H3 mutant. Three reference strains were also analyzed in the same way which expressed the wild-type histone protein. All strains were handled in the same way. A fresh culture of each strain was inoculated from a saturated overnight culture and grown to an OD A600 of approximately 0.7. Cells were harvested and total RNA extracted.