Abstract: The present invention is directed to compositions and methods for producing avermectins, and is primarily in the field of animal health. The present invention relates to the identification and characterization of two novel genes, herein referred to as the aveR1 and aveR2 genes, that are involved in regulating avermectin polyketide synthase (PKS) expression and avermectin biosynthesis in Streptomyces avermitilis. The present invention is based on the discovery that inactivation of these genes results in an increase in the amount of avermectin produced by S. avermitilis.

Abstract: The present invention describes the DNA sequence for eukaryotic genes encoding &egr; cyclase, isopentenyl pyrophosphate (IPP) isomerase and &bgr;-carotene hydroxylase as well as vectors containing the same and host cells transformed with said vectors. The &egr; cyclase and &bgr;-carotene hydroxylase genes disclosed include those from A. thaliana; the IPP isomerase genes disclosed include those from A. thaliana, H. pluvialis, and marigold. The present invention also provides methods for controlling the ratio of various carotenoids in a host cell and for the production of novel carotenoid pigments. The present invention also provides a method for screening for eukaryotic genes encoding carotenoid biosynthesis enzymes.