Berry B T, Ghosh A K, Kumar D V, Spodick D A, Roy-Burman P
Department of Pathology, University of Southern California School of Medicine, Los Angeles 90033.
J Virol. 1988 Oct;62(10):3631-41. doi: 10.1128/JVI.62.10.3631-3641.1988.
The nucleotide sequence of the 5' long terminal repeat (LTR) of three independent loci (CFE-6, CFE-16, and CF-14) of endogenous feline leukemia virus (FeLV) DNAs of the domestic cat genome was determined. The 3' LTR of the CFE-6 clone was also sequenced. The endogenous FeLV LTRs, which were very similar to each other in sequence and in organization of the functional domains, differed considerably from the exogenous FeLV LTR in the U3 region. The major differences in U3 included variations in sets of small (14 to 19 base pair) direct repeats, altered location of the simian virus 40 core enhancer-like sequence, and occurrence of three segments of largely nonhomologous sequences. There was extensive homology between endogenous and exogenous FeLV LTRs in sequences beginning from the TATA box through the R region down to the 3' end of the U5 region. The DNA sequence downstream of the 5' LTR encompassing the primer-binding site, leader, and almost to the end of the p15gag coding region, a point up to which the sequencing was carried out, also revealed a high degree of conservation. However, the detection of frameshift and nonsense mutations in this region of a nearly full-length endogenous provirus sequence (CFE-6) predicted its defectiveness and correlated with the lack of infectivity of this DNA. The functional studies of the endogenous LTRs, based on linkage to the bacterial cat gene and transient expression in feline cell lines, indicated that although the basic characteristics for promotion and enhancement of transcription were retained in each LTR, there was a significant variation in the activity of the cat constructs. Reconstruction and deletion analyses with the CFE-6 5' LTR revealed the presence of strong transcription regulatory sequences in the 702-base-pair region immediately upstream of the 5' boundary of the endogenous LTR. These and related data suggest that in addition to the transcription-modulating elements occurring within the LTR, the cis-acting nucleotide sequences in the upstream cellular DNA may determine the overall efficiency of transcription of the defective endogenous FeLV provirus loci of the felid genome.
测定了家猫基因组内源性猫白血病病毒（FeLV）DNA三个独立位点（CFE - 6、CFE - 16和CF - 14）的5'长末端重复序列（LTR）的核苷酸序列。还对CFE - 6克隆的3' LTR进行了测序。内源性FeLV LTR在序列和功能域组织上彼此非常相似，但在U3区域与外源性FeLV LTR有很大差异。U3中的主要差异包括小（14至19个碱基对）直接重复序列组的变化、猿猴病毒40核心增强子样序列位置的改变以及三个大部分非同源序列片段的出现。从TATA框到R区域直至U5区域3'端的序列中，内源性和外源性FeLV LTR之间存在广泛的同源性。5' LTR下游包含引物结合位点、前导序列以及几乎到p15gag编码区末端（测序进行到该点）的DNA序列也显示出高度保守性。然而，在一个近乎全长的内源性前病毒序列（CFE - 6）的该区域检测到移码和无义突变，预测其有缺陷，并与该DNA缺乏感染性相关。基于与细菌猫基因的连接和在猫细胞系中的瞬时表达对内源性LTR进行的功能研究表明，尽管每个LTR都保留了促进和增强转录的基本特征，但猫构建体的活性存在显著差异。对CFE - 6 5' LTR进行的重建和缺失分析揭示，在内源性LTR 5'边界上游紧邻的702个碱基对区域存在强转录调控序列。这些及相关数据表明，除了LTR内的转录调节元件外，上游细胞DNA中的顺式作用核苷酸序列可能决定猫科动物基因组中有缺陷的内源性FeLV前病毒位点转录的整体效率。
