Detection of a countertranscript in promyelocytic leukemia cells HL60 during early differentiation by TPA

We have isolated several cDNA clones corresponding to the mRNAs expressed during early phase of differentiation of promyelocytic leukemia cells HL60 by TPA. Two interrelated clones were examined, one pHH81 and the other pHH58 possessing inserts of 180 and 730 base pairs, respectively. Northern blot analyses of poly(A) RNAs from induced cells revealed that the clone pHH81 hybridized with 4.3kb RNA, while the clone pHH58 hybridized with 4.3kb and, in addition 0.7kb RNA. Sequence determination of those cDNA clones and extensive Northern blot analyses revealed that the inserts of these clones were derived from 4.3kb mRNAs. 0.7kb RNA was hybridized with only 5' upstream region of the clone pHH58, especially with the strand designed to detect anti-sense RNA. Thus we concluded that 0.7kb RNA is a countertranscript of 4.3kb RNA expressed during early differentiation of HL60 cells.