Sequence and expression of Drosophila myristoyl-CoA: protein N-myristoyl transferase: evidence for proteolytic processing and membrane localisation

The enzyme N-myristoyl transferase transfers the 14 carbon fatty acid myristate to an N-terminal glycine residue in a small subset of cytoplasmic proteins. Many myristoyl proteins are components of cellular signalling pathways, some of which play important roles during embryonic development, for example protein kinase A. Thus, the function of N-myristoyl transferase is probably essential for embryogenesis and it is of some interest to study the enzyme in an organism with well understood developmental biology. In this paper we report the purification of a processed form of the Drosophila enzyme from peripheral membrane fractions of embryos by affinity chromatography to a protein containing leucine rich repeats. We have also isolated the Drosophila N-myristoyl transferase gene and determined its nucleotide sequence. The predicted amino acid sequence of the Drosophila enzyme is closely related to that of mammalian and fungal N-myristoyl transferases and residues essential for enzyme function are conserved. Our findings indicate that a fraction of Drosophila NMT is bound to the membrane and they are consistent with recent results for the human enzyme. We suggest that N-myristoyl transferase may be recruited to the membrane as part of a translational complex, perhaps by binding to p34 ribosome binding protein, a leucine rich repeat receptor of the microsomal membranes. We have also studied the expression pattern of the gene in the embryo by northern blot analysis and in situ hybridization. The transcripts appear to be uniformly distributed in the pre-cellular embryo but at later stages the RNA is barely detectable with these methods. However, from about stage 14, high levels of transcript are detected in a small number of randomly distributed cells of the central and peripheral nervous system.