The enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase in Drosophila melanogaster synthesizes mevalonate for the production of nonsterol isoprenoids, which are essential for growth and differentiation. To (Mr, 98,165) that was similar to the hamster HMG CoA reductase. The C-terminal region had 56% identical residues and the N-terminal region had 7 potential transmembrane domains with 32 to 60% identical residues. In hamster HMG CoA reductase, the membrane regions were essential for posttranslational regulation. Since the Drosophila enzyme is not regulated by sterols, the strong N-terminal similarity was surprising. Two HMG CoA reductase mRNA transcripts, -3.2 and 4 kilobases, were differentially expressed throughout Drosophila development. Mevalonate-fed Schneider cells showed a parallel reduction of both enzyme activity and abundance of the 4-kilobase mRNA transcript.Cholesterol is important for structural purposes in the membranes of vertebrates, but recent studies have also elucidated its role in regulating the expression of certain genes (5). The rate-controlling enzyme for cholesterol synthesis, 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, is regulated by cholesterol in a complex pattern with both transcriptional (28, 34) and posttranslational (8, 19) mechanisms. As a typical housekeeping gene, the HMG CoA reductase gene is usually transcriptionally active. Its steady-state activity is subject to multivalent feedback suppression (4) by at least two classes of metabolic products derived from its immediate product, mevalonate. Cholesterol, the major mevalonate-derived product of mammalian cells, suppresses both HMG CoA reductase activity and its mRNA levels in cultured cells (10) and rat liver (26). Pretreatment of cells with cholesterol also prevented transcription from the gene in isolated nuclei (28), and the hamster HMG CoA reductase promoter remained cholesterol sensitive when transfected into cultured cells (34). Posttranslational regulation was revealed by the accelerated degradation of the enzyme in response to exogenous cholesterol (8). Thus, cholesterol has regulatory effects in both the nucleus and cytoplasm.Owing to the rapid and high conversion of mevalonate to sterols in mammals, it has been difficult to assess the sterol-independent regulatory pathway of HMG CoA reductase. Studies of this pathway suggested that the basal regulation was mediated by unidentified nonsterol mevalonate derivatives (16,47 Like the mammalian enzyme, the HMG CoA reductase of cultured Drosophila cells (Kc and Schneider cells) appears to be a microsomal enzyme whose activity is modulated by the addition of exogenous mevalonate. In contrast to the hamster enzyme, exogenous sterols have no effect upon the Drosophila HMG CoA reductase (3,32,43) and thus allow a clear separation of the sterol and nonsterol regulatory pathways. Since insects lack the ability to synthesize sterols and their HMG CoA reductase is insensitive to sterol regulation, one might conclude that insects either lost or neve...

Cytoplasmic microinjection of murine Mx mRNA synthesized in vitro or nuclear microinjection of Mx cDNA under the control of a constitutive promoter into murine Mx- cells led to the accumulation of Mx protein in the nucleus and inhibited the replication of influenza virus but not of vesicular stomatitis virus (VSV). Similar results were also found with dog, rat, chicken, and monkey cells. A human lung fibroblast cell line (A549) was exceptional in that Mx protein was located predominantly in the cytoplasm and showed antiviral activity. Truncation of the 19 last residues of murine Mx protein almost completely abolished accumulation of Mx protein in the nucleus; however the activity against influenza virus was at least partially retained. The truncated region contains a segment rich in basic amino acids, similar to that reported for several nuclear location signals.

The rat alpha- and bovine alpha s1-casein genes have been isolated and their 5' sequences determined. The rat alpha-, beta-, gamma- and bovine alpha s1-casein genes contain similar 5' exon arrangements in which the 5' noncoding, signal peptide and casein kinase phosphorylation sequences are each encoded by separate exons. These findings support the hypothesis that during evolution, the family of casein genes arose by a process involving exon recruitment followed by intragenic and intergenic duplication of a primordial gene. Several highly conserved regions in the first 200 base pairs of the 5' flanking DNA have been identified. Additional sequence homology extending up to 550 base pairs upstream of the CAP site has been found between the rat alpha- and bovine alpha s1-casein sequences. Unexpectedly, the 5' flanking promoter regions are conserved to a greater extent than both the entire mature coding and intron regions of these genes. These conserved 5' flanking sequences may contain potential cis regulatory elements which are responsible for the coordinate expression of the functionally-related casein genes during mammary gland development.

The enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase in Drosophila melanogaster synthesizes mevalonate for the production of nonsterol isoprenoids, which are essential for growth and differentiation. To understand the regulation and developmental role of HMG CoA reductase, we cloned the D. melanogaster HMG CoA reductase gene. The nucleotide sequence of the Drosophila HMG CoA reductase was determined from genomic and cDNA clones. A 2,748-base-pair open reading frame encoded a polypeptide of 916 amino acids (Mr, 98,165) that was similar to the hamster HMG CoA reductase. The C-terminal region had 56% identical residues and the N-terminal region had 7 potential transmembrane domains with 32 to 60% identical residues. In hamster HMG CoA reductase, the membrane regions were essential for posttranslational regulation. Since the Drosophila enzyme is not regulated by sterols, the strong N-terminal similarity was surprising. Two HMG CoA reductase mRNA transcripts, approximately 3.2 and 4 kilobases, were differentially expressed throughout Drosophila development. Mevalonate-fed Schneider cells showed a parallel reduction of both enzyme activity and abundance of the 4-kilobase mRNA transcript.