Two major sequence classes of ribosomal RNA genes in Plasmodium berghei

Primary sequence differences have been found between two different ribosomal DNA (rDNA) units of the rodent malaria parasite, Plasmodium berghei, within the coding areas of both the small and large ribosomal RNAs (rRNA). The coding regions of rDNA unit A are protected from nuclease S1 digestion by rRNA isolated from asexual blood stage parasites. Under the same conditions of analysis, the comparable coding regions from unit C are cut into small pieces by nuclease S1, the largest being 1.1 kb. Analysis of heteroduplexes of the respective DNA clones from units A and C by electron microscopy reveals that the two units differ in the 5' flanking and internal transcribed sequences and that there are extensive sequence differences in the DNA coding for the mature large rRNA. No introns were detected in either rDNA unit. The data shows that unit A is transcribed in blood stage parasites and that unit C is not.