The adaptational system as a dynamical feedback system

Growth hormone receptor is a cytokine-type receptor which is required for normal somatic growth and for numerous metabolic processes. Its complementary DNA (cDNA) has been isolated in various species leading to intensive studies to elucidate the mechanism of action of the growth hormone. However, serious difficulties have been reported in cloning in Escherichia coli, an intact full-length human cDNA. In this study, the cDNA is shown to contain a cryptic bacterial promoter driving inappropriate expression of a part of human growth hormone (hGH) receptor which is toxic for E. coli growth. Identification of this promoter and its inactivation by changing only one nucleotide led us to obtain stable bacterial clones containing a high copy number of full-length coding sequences. This molecular clone was used in a baculovirus/insect cell system to produce large amounts of glycosylated recombinant receptor. Binding studies with 125I-labelled hGH revealed an affinity constant of 2.8 x 10(9) M(-1), similar to that reported for the native liver receptor. This report described a general method of cloning which could be applied to similar unclonable cDNA fragments.