Construction of cDNA Clone and Nucleotde Sequence of RNA3 of Cucumber Mosaic Virus Isolate Xb from Banana

The nucleotide sequence of RNA3 of a cucumber mosaic virus strain from banana of subgroup Ⅱ(CMV-Xb) was cloned and analyzed at nucleotide and protein level after RT-PCR amplificaion with two pairs of primers.The results showed that CMV-Xb is composed of 2205 nucleotides(nt) with two open reading frames.The one near 5'termini(97～936nt) encodes a 3a protein with 279 amino acids(aa),the other near 3'termini (1225～1871nt)codes for coat protein with 218aa,The 5'non-coding region(NR),intercistron region(IR) and 3'NR are 96nt,288nt and 324nt, respectively.Comparison at the nucleotide and putative amino acid level with other strains in subgroup Ⅱ showed that the nucleotide sequence of Xb is very conservative in the encoding regions as well as non-coding regions.The evolution of RNA3s of subgroup Ⅱ members of CMV is consecutive.