DERIVATION AND PARTIAL ANALYSIS OF 2 HIGHLY-ACTIVE MYELOMA CELL TRANSFECTANTS

Vectors have been designed to optimise the expression of heterologous proteins in transfected mouse myeloma cells. The over-ridingly importa nt DNA element contained in these constructs is the classical mouse im munoglobulin heavy chain enhancer. It is shown that even in the absenc e of a well-known promoter element, the enhancer can drive gene expres sion in stable cell transfectants and the main transcriptional start s ite utilized in such situations has been mapped to within the previous ly defined enhancer region. Using chicken lysozyme as a reporter funct ion in these vectors, two transfected myeloma cell clones have been is olated which secrete this protein at levels 50-100-times as high as th ose usually obtained with the same vectors and it is shown that in mol ar terms this is at least as high as endogenous immunoglobulin produce d by a related line. Analysis of these lines show that in one case onl y a single copy, and in the other two to three copies, of the apparent ly unrearranged vector have integrated at a single locus within the ge nome. Possible explanations for the high-level expression are discusse d.