The Nature of a Copia - Like Transposable Element Inserted in a Baculovirus = The Nature of a Copia - Like Transposable Element Inserted in a Baculovirus

다국어 초록 (Multilingual Abstract)

Baculoviruses possess large (∼ 100 Kilobase pair), double-stranded, circular DNA genome which are packaged in enveloped, rod-shaped capsids. A mutant of the baculovirus Autographa californica nuclear polyheadrosis virus (AcNPV) was recently isolated following serial passage of the virus through a cell line of the lepidopteran insect Trichoplusia ni. The mutant, known as FP-D, has a most unusual genotype; restriction endonuclease analysis of the viral DNA reveals the presence of a genetically unstable sequence inserted in the mutant DNA. Further analysis has established that this sequence is a mobile genetic element of T. ni and is a member of the copia-like class of transposable elements. We call the element TE-D. TE-D is 7.3 Kilobases (Kb) in length and contains 0.27 Kb direct terminal repeats so that its structure is similar to copia-like elements of Drosophila as well as the evolutionarily related retroviruses of vertebrates. The TE-D sequence is genetically unstable; a second virus, referred to as FP-DS, arises spontaneously and at high frequency in FP-D infected cells. FP-DS contains only one of the two 0.27 Kb terminal repeats of TE-D and may arise from recombination between the direct terminal repeats of TE-D. We also have evidence that the element exists in free linear and circular form in FP-D infected cells; transposition of the element may therefore involve a 7.05 Kb circular and/or linear intermediate. TE-D is a mid-repetitive, dispersed element of T. ni cells. It is found in 45 or 50 different locations in the T. ni genome. The element is mobile as determined by experiment in which the position of TE-D sequences have amplified several fold and the internal sequences of TE-D have diverged slightly. We are currently investigating the effects of element insertion on viral transcription and have observed the enhancement of transcription of viral sequences next to terminal repeats. FP-D will be a very valuable tool for studying transposable element movement and expression. We have a permissive insect cell line, S. frugiperda, which lacks TE-D so that the element can be studied in a naive cell environment. We expect that an analysis of FP-D will help to define the relationship between copia-like transposable elements and retroviruses.