Interspersed Homologous DNA of Autographa californica Nuclear Polyhedrosis Virus Enhances Delayed-Early Gene Expression

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Abstract
The five regions of homologous DNA which are interspersed in the genome of the baculovirus Autographa californica nuclear polyhedrosis virus increased the expression of a delayed-early gene of this virus. Although this activity was first observed as a 10-fold trans effect, the homologous region 5 ( hr 5) enhanced the expression of linked genes 1,000-fold. The hr 5 enhancer also exhibited the other characteristics associated with viral enhancer elements, including orientation independence and the abilities to function at a distance from the linked promoter, to regulate heterologous promoters, and to increase the number of RNA polymerase molecules transcribing the linked genes. The expression of the immediate-early regulatory gene was not enhanced by cis -linked hr 5, although the enhancer function may require the immediate-early regulatory gene product. The hr 5 enhancer was relatively insensitive to competition by an excess of enhancer molecules. The nucleotide sequence of hr 5 revealed two different conserved repeats separated by nonhomologous DNA. Deletion analysis of the hr 5 enhancer indicated that a 30-base-pair inverted repeat was essential for enhancer function.