Different cap 1 : cap 2 ratios in rabbit α and β globin mRNA

Abstract

CAP structures type 0 (m⁷G⁵′ppp⁵′X), type 1 (m⁷G⁵′ppp⁵′XmY), and type 2 (m⁷G⁵′ppp⁵′XmYmZ), differing in the number of 2′-O-methylated penultimate nucleotides, have been found at the 5′ termini of many viral and non-viral eukaryotic messenger RNAs¹. The ability to quantitatively remove the m⁷G⁵′ppp-blocking group from eukaryotic mRNAs and to subsequently label their 5′ termini with ³²P using [γ-³²P]ATP and T₄ poly-nucleotide kinase has led to the determination of nucleotide sequences present at the 5′ termini for rabbit α and β globin mRNA^2,3 and alfalfa mosaic virus RNA 4 (ref. 4). The first six nucleotides of both rabbit α and β globin mRNA are identical and these two mRNAs each contain a mixture of cap types 1 (m⁷G⁵′ppp⁵′m⁶AmC) and 2 (m⁷G⁵′ppp⁵′m⁶AmCmA), differing only by the 2′-O-methylation of their penultimate C residues2. This 5′-end labelling procedure can also be used to determine the relative amounts of cap types for each individual rabbit globin mRNA, without having to first purify each mRNA to homogeneity². In this work the cap 1 : cap 2 ratios have been determined. The results indicate a two- to threefold enrichment of type 1 cap structures in α relative to β mRNA.