NONSYMMETRICAL CYTOSINE METHYLATION IN TOBACCO POLLEN DNA

We have detected sequence-specific non-symmetrical cytosine methylatio n within a 140 bp region of the promoter for the tobacco auxin-binding protein gene T85 in pollen DNA. Direct sequencing of the population o f bisulphite reaction products showed that, in this region, 10 out of a possible 49 cytosine residues were methylated at a high frequency in pollen whereas the corresponding region from somatic cells (leaf DNA) did not show a detectable level of methylation. The context of these sites was 1 x m(5)CpTpC, 1 x m(5)CpGpT, 1 x m(5)CpCpT, 2 x m(5)CpTpT, 2 x m(5)CpGpG, and 3 x m(5)CpApT of which only m(5)CpGpG and m(5)CpGpT fitted the consensus sequence for symmetrical methylation in plants.