Genetic Expression and Postnatal Development of the Brain: Some Characteristics of Nonpolyadenylated mRNAs

Despite the enormous complexity of the brain, progress is being made in understanding the molecular biology of this organ. The sequence complexity of polyribosomal RNA from the mammalian (rodent) brain has been estimated to be about 2 × 105 kb and is composed of polyadenylated and nonpolyadenylated RNA populations of similar complexity (Chikaraishi 1979; Van Ness et al. 1979). The existence of a complex class of RNA molecules lacking poly(A) was first suggested from measurements of the sequence complexity of total brain polysomal RNA versus the poly (A)+ RNA fraction of polysomal RNA. Initial observation on mouse (Van Ness et al. 1979) and rat (Chikaraishi 1979) brain polyribosomes showed that polysomal RNA was about twice as complex as the poly(A)+ RNA fraction, as measured by RNA-driven hybridization of single-copy genomic DNA. The kinetics of hybridization of cDNA complementary to polysomal poly (A)− RNA also indicated a complexity estimate similar to...