Abstract: D1 DNA and its partial upstream sequence in the first intron of the hsp70 gene from three rice species (Oryza sativa L. ssp. indica, 0. sativa L. ssp. japonica and 0. rufipogon W. Griffith) were sequenced and compared, and the D1 snoRNA encoded by D1 DNA was also identified by Northern hybridization and cDNA sequencing. D1 snoRNA, with a 14 nucleotides (nts) complementary to rice 25S rRNA, belongs to the antisense snoRNA family, and is suggested to guide the methylation of the 807th nucleotide position in rice 25S rRNA. The distance between D1 DNA and C1 DNA was only 105 nts. It was demonstrated that two snoRNA in an intron continually encoded within such a short region was a rare case, which provided us with a good system to study the processing mechanism of posttranscription of snoRNAs in tandem structure.

Key words: D1 snoRNA, Intron, Methylation, Rice