HIGH-COPY EXPRESSION VECTOR BASED ON AMPLIFICATION-PROMOTING SEQUENCES

We describe a new vector system that allows efficient expression of he terologous proteins in transformed mouse L fibroblasts. This is due to its persistence at high copy numbers, achieved by a 370-bp amplificat ion promoting element (muNTS1) derived from the nontranscribed spacer of murine rDNA. Copy number determination showed that this sequence me diates a 40- to 800-fold amplification of the vector DNA in transfecte d L cells. High copy number was accompanied by increased expression le vels of the reporter gene secreted alkaline phosphatase (SEAP). Analyz ing the structural organization of multicopy plasmid DNA in mouse L ce lls revealed that plasmid DNA is integrated as reiterated head-to-tail concatamers into the chromosomal DNA. The vector described here can b e used as a versatile high-copy expression system for heterologous pro teins overcoming any limitation to enzyme-deficient cell lines.