Department of Genetics, Monash University, 3168, Clayton, Victoria, Australia.
Plant Mol Biol. 1986 Jan;6(1):33-9. doi: 10.1007/BF00021304.
Ribosomal RNA genes of Lilium henryi are almost completely methylated at CG and CNG sequences. A short under-methylated region was detected between 2.05 and 2.4 kbp upstream of the 18S sequences. It included the only sites of digestion by four methylation-sensitive restriction endonucleases - PstI, Hae II, Eco RII and Hpa II. Only about 15%-20% of rDNA repeats from shoot meristem are susceptible to each of the enzymes. The same repeats are apparently cut by all enzymes and occur in contiguous blocks. Because the region involved is likely to include regulatory sequences it may be that under-methylation occurs specifically in active rDNA repeats. To test this, rDNA was examined from pollen mother cells at pachytene where transcription has fallen to near zero. Under-methylation levels here were similar to those in shoot meristem tissue. Thus methylation of this region is not the agent responsible for rDNA gene inactivation in pachytene cells and it does not occur immediately genes become inactive. Even so, sequences in this region might be prevented from becoming methylated in transcribing repeats.
百合属亨利的核糖体 RNA 基因在 CG 和 CNG 序列上几乎完全甲基化。在 18S 序列上游 2.05 到 2.4 kbp 处检测到一个短的低甲基化区域。它包括四个甲基化敏感的限制内切酶 - PstI、Hae II、Eco RII 和 Hpa II 的唯一消化位点。只有大约 15%-20%的芽分生组织的 rDNA 重复序列容易受到每种酶的影响。相同的重复序列显然被所有酶切割，并发生在连续的块中。由于所涉及的区域可能包括调节序列，因此低甲基化可能专门发生在活性 rDNA 重复序列中。为了验证这一点，对处于粗线期的花粉母细胞中的 rDNA 进行了检查，此时转录几乎降至零。此处的低甲基化水平与芽分生组织组织中的相似。因此，该区域的甲基化不是导致粗线期细胞中 rDNA 基因失活的原因，它不会立即发生在基因失活时。即便如此，转录重复序列中的这些区域可能会被阻止甲基化。
