Influenza virus strain A/PR/8/34(H1N1)acquired a high-yielding property after serial passages in fertilized eggsSix internal RNA segments of the high-yielding strain were sequenced from their cloned cDNAs and compared with the corresponding original sequences in the prime A/PR/8/34(H1N1)strainNinety-three point mutations were found accumulated in six genes(PB2,PB1,PA,NP,M,and NS),which lead to 27 amino acid changesA significant low mutation frequency without amino acid change was observed in PA geneThe mutation frequency at the amino acid level was the highest(about 3%)in M2 proteinOur data suggest that the unequal distribution of mutations among different viral proteins may correlate with individual role of each protein in viral
