FIXING HUMAN FACTOR-IX (FIX) - CORRECTION OF A CRYPTIC RNA SPLICE ENABLES THE PRODUCTION OF BIOLOGICALLY-ACTIVE FIX IN THE MAMMARY-GLAND OFTRANSGENIC MICE

Transgenic mice and sheep secrete only low levels of human factor IX i n their milk because of an aberrant splicing of the transgene RNA in t he mammary gland. Removal of the cryptic 3' splice site prevents this splicing and leads to the production of relatively high levels of fact or IX. The purified protein is fully active showing that the mammary g land is capable of the efficient post-translational modification of th is protein and that transgenic animals are a suitable means of its pro duction.