[Uncoordinated expression of B2+mRNAx and other types of B2-containing poly(A)+RNA in various mouse tissues]

Northern blot hybridization of nuclear, cytoplasmic and polysomal poly(A)+RNAs from different normal and tumor mouse cells was carried out with labelled separated DNA strands of the cloned cDNA fragment containing repetitive B2-element. Several important results were obtained in these experiments: (i) while nuclear RNAs contain copies from both strands of B2 element, only one strand ("canonical" orientation) of B2 can be detected in the mature cytoplasmic poly(A)+RNAs of all mouse tissues studied, (ii) the abundant 2 kb B2+mRNAx is tissue-specific for mouse liver and kidney cells, its transcription is greatly increased in regenerating liver and completely abolished in hepatoma, (iii) an elevated level of small B2+RNAs and 1.6 kb B2+RNA in some tumor cells is observed, (iv) differential transcription of the major classes of B2+RNAs in different mouse tissues suggests the non-coordinated regulation of their expression.