Clark S P, Mak T W
J Virol. 1984 Jun;50(3):759-65. doi: 10.1128/JVI.50.3.759-765.1984.
Comparison of the genomic sequences of the Friend spleen focus-forming virus with other murine retroviral sequences indicated that the spleen focus-forming virus was derived from at least three retroviruses. The 5' end of the virus, from the primer binding site through most of gag, was derived from AKV. The rest of gag and all of pol were of uncertain origin, but were probably derived from the same xenotropic virus that gave rise to the 5' half of env. The remainder was derived from Friend murine leukemia virus. The positions of a 585-base deletion, a 6-base duplication, and a point insertion that leads to a frame shift and premature protein termination in the ecotropic 3' end of env were invariant between three spleen focus-forming virus strains, indicating that they had a single common ancestor. However, the point of crossover between xenotropic viral sequences and Friend murine leukemia virus was different in each strain, and two strains were much more closely related to each other than to the third in the xenotropic region, indicating that these strains had diverged by multiple recombinations. Furthermore, a different nucleotide comprised the single point insertion near the 3' end of env, suggesting that these viruses have an extremely high transition and transversion rate.
对弗瑞德脾集落形成病毒与其他鼠逆转录病毒序列的基因组序列进行比较表明，脾集落形成病毒源自至少三种逆转录病毒。病毒的5'端，从引物结合位点到大部分gag基因，源自AKV。gag基因的其余部分和所有pol基因来源不明，但可能源自产生env基因5'端一半的同嗜性病毒。其余部分源自弗瑞德鼠白血病病毒。在三个脾集落形成病毒株中，env基因嗜亲性3'端的一个585碱基缺失、一个6碱基重复和一个导致移码和蛋白质过早终止的点插入的位置是不变的，这表明它们有一个共同的祖先。然而，每个毒株中异嗜性病毒序列与弗瑞德鼠白血病病毒之间的交叉点不同，并且在异嗜性区域中，两个毒株彼此之间的关系比与第三个毒株更为密切，这表明这些毒株通过多次重组而分化。此外，env基因3'端附近的单点插入由不同的核苷酸组成，这表明这些病毒具有极高的转换和颠换率。
