Enhancement of protein expression in insect cells by a lobster tropomyosin cDNA leader sequence.

We describe a cis element that dramatically increases the expression levels of exogenous genes in baculovirus-infected insect cells. This 21 bp sequence element is derived from a 5' untranslated leader sequence of a lobster tropomyosin cDNA (L21). By using a transfer vector carrying L21, the expression levels of tropomyosin and luciferase were 20- and seven-fold higher with L21 than without L21, respectively. L21 has both the Kozak sequence and the A-rich sequence found in the polyhedrin leader sequence. We assume that both sequence elements are essential for the enhancement of protein expression in the baculovirus-based expression system.