Polycytidylic Acid Tract

The poly(C) tract first described by Porter et (13) appears to be present only in the cardio- and FMD viruses (14) The length of the poly(C) tract varies between different isolates of the same virus. Ihis was first noted for different FMDV serotypes (14) and has since been observed with a virulent and an attenuated strain of each of two different serotypes of the viinis (15 Hobson, K.J.H., unpublished obsecrations). It may be significant that with each of the serotypes, the length of the poly(c) tract of the attenuated strain was only about one half of the length of that in the virulent strain. 

The vaxiability in the length of the poly(c) tract is not confined to PMDY-EITA. In some recent experiments at Pirbright, 

Stephenson and D.J. Rowlands have found that the length of the poly(c) tract varies between 50 and 500 nucleotides in six different isolates of encephalomyocarditis virus. The results of one dimensional polyacrylamide gel electrophoresis of the ribonuclease T hydrolysates of the six RNAs are shown in Table 1. 

Unlike the poly(A) tract of the picornavirus RUAs, which gives a heterogeneous band in one dimensional polyacrylamide gel electrophoresis, the poly(c) tract is usually a sharp, well defined band, suggesting that the length is homogeneous for an individual virus RRA. Similarly, in two dimensional electrophoretic separations, the poly(c) tract is found as a small spot whereas the poly(A) tract is present as an elongated spot. 

As mentioned by Pellner (chapter 2), the poly(c) tract in both the PMBV and cardiovirus RRA is situated near the 5 eiid of the 

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