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hibited by actinomycin D and pyrophosphate while the product was insensi
tive to pancreatic RNase digestion yet it was sensitive to snake venom
phosphodiesterase and alkaline hydrolysis. However, they were able to
show by nearest neighbor analysis that the product was poly C.
The products of the CTP incorporating activity for this study were
isolated by phenol extraction followed by ethanol precipitation of the
aqueous phase. The size of the isolated products as determined by their
elution position from a Biogel P-4 column indicated they comprised two
classes of molecules with mean molecular weights of 800 and 680 respect
ively (Figure 4). These molecules have absorbancy spectra very similar
if not identical to that of CpC which suggests that cytosine is the only
base incorporated into the products. The snake venom phosphodiesterase
clevage product of both molecular weight classes is 5'-CMP, the expected
clevage product of poly C of CpC. The CTP incorporating products showed
no sensitivity to pancreatic RNase A. The possibility exists that these
molecules are di- or trinucleotides of CMP which have modified 3' terminus
which prevents the RNase A from binding to the molecules. All attempts
, 3
to demonstrate that the products of the H-CTP incorporating activity could
be CDP-diglyceride gave negative results.
Recent studies have demonstrated the presence of an unusual structure
viral messenger RNAs in which the 5' end of the messenger RNA is blocked
by a 7-methyl guanosin linked to a 2'0-methylated nucleotide, Nm, through
a 55 pyrophosphate bond (186,187). The 2'-0-methylated nucleotide Nm
is linked to the adjacent nucleotide M by a 3'5' phosphodiester bond.
These blocked, methyoated 5'-termini ("caps") are resistant to digestion
by ribonuclease. The possibility exists that the labeled products obtained