Androgen-regulated ornithine decarboxylase mRNAs of mouse kidney

Ornithine decarboxylase, the first enzyme of the polyamine biosynthetic pathway, is induced by androgens in the mouse kidney. We have isolated from a kidney cDNA clone bank two plasmids, pODC1440 and pODC934 , that contain different cDNA inserts corresponding to ornithine decarboxylase mRNA. Identification was based upon the ability of plasmid-specific mRNAs to encode a 53,000-dalton polypeptide that reacts with antibody to purified mouse kidney ornithine decarboxylase. Plasmid pODC1440 hybridizes predominantly to a mRNA that is 2.1 kilobases (kb) long and is induced about 20-fold in the kidneys of female mice treated with testosterone. Plasmid pODC934 hybridizes to mRNAs of lengths 2.2 and 2.6 kb, which are induced about 8-fold by testosterone. There are probably no more than 1-2 copies of the pODC1440 -specific sequence in the mouse genome, while there may be as many as 12 copies of the pODC934 -specific sequence. That the two plasmids correspond to different ornithine decarboxylase mRNAs is suggested by two observations. First, several mouse strains express normal levels of pODC934 -specific RNA and little or no pODC1440 -specific RNA; furthermore, pODC934 -specific RNA is expressed in several tissues while pODC1440 -specific RNA is kidney-specific. Thus, androgen-mediated stimulation of kidney ornithine decarboxylase activity levels involves alterations in the concentrations of at least two distinct mRNAs.