Heterogeneous nuclear RNA (hnRNA)- The primary precursor mRNA transcript made in the eukaryotic nucleus are called "hnRNA," an abbreviation for "heterogeneous nuclear RNA. Features are as follows:
Introns: Since many eukaryotic nuclear genes are interrupted by introns, RNA transcripts of intron-containing genes have intronic RNA sequences.
Poly A tails at the 3'-end: Poly A tails added to the 3'-end of most, but not all hnRNAs during nuclear RNA processing. These tails are retained in the processed mRNA.
5'-Cap structure: A modified GTP is covalently attached to the 5'-end of most precursors to mRNA. This cap structure is also retained in the processed mRNA.
Base Composition and relation to template strand: RNA is synthesized from a DNA template. The sequence of the RNA is complementary to the DNA template strand, and opposite in polarity. C and T in the DNA template are transcribed by RNA polymerase as G and A in the hnRNA, respectively. A and G in the DNA template are transcribed as U and C in hnRNA. Thus hnRNA and mRNA are sequences of A, G, C and U's.
Introns: Since many eukaryotic nuclear genes are interrupted by introns, RNA transcripts of intron-containing genes have intronic RNA sequences.
Poly A tails at the 3'-end: Poly A tails added to the 3'-end of most, but not all hnRNAs during nuclear RNA processing. These tails are retained in the processed mRNA.
5'-Cap structure: A modified GTP is covalently attached to the 5'-end of most precursors to mRNA. This cap structure is also retained in the processed mRNA.
Base Composition and relation to template strand: RNA is synthesized from a DNA template. The sequence of the RNA is complementary to the DNA template strand, and opposite in polarity. C and T in the DNA template are transcribed by RNA polymerase as G and A in the hnRNA, respectively. A and G in the DNA template are transcribed as U and C in hnRNA. Thus hnRNA and mRNA are sequences of A, G, C and U's.
