Human placental lactogen has been found to resemble human pituitary growth hormone very closely in amino acid sequence, about 80% of the residues examined being identical in the two molecules when a revised sequence for growth hormone is used as the basis for comparison. The structural features responsible for the differing biological potency of the two hormones may therefore reside in rather limited regions of primary structure. The observation of internal sequence homologies within the pituitary growth hormone and prolactin and the placental lactogen molecules suggests that these polypeptide hormones may have evolved by genetic reduplication from a smaller common ancestral peptide. This finding directs further attention to subfragments of these molecules as possible possessors of intrinsic somatotrophic and lactogenic activity.Previous studies on pituitary growth hormone and prolactin, and on placental lactogen, have demonstrated a close structural similarity within this group of hormones, and thus provided a basis for their shared biological and immunological properties (1-6). However, complete amino acid sequences have been reported so far only for human growth hormone (1) (growth hormone) and ovine prolactin (3) (prolactin), and detailed intra-species comparisons of structure have not been possible. Recently, we have extended earlier structural studies (2, 5) on human placental lactogen (lactogen) and have determined much of its amino acid sequence. In the course of this work it was noted that discrepancies existed between the amino acid sequence of growth hormone as previously reported by Li and coworkers (1), and that which would have been predicted by homology with the structure of lactogen as determined in our laboratory. This led us to postulate an error in the previous growth hormone sequence, and to undertake a reinvestigation of its primary structure. Our results (7) showed that the previous aminoterminal structure of growth hormone was in fact incorrect, and that a sequence of 15 amino acids containing the single tryptophan of growth hormone, assigned by Li and coworkers to positions 17-31, must reside elsewhere in the molecule, most probably occupying positions 77-91. Our more recent investigations (manuscript in preparation) of the growth-hormone sequence have confirmed that this is indeed the correct location for the tryptophan sequence, and have also demonstrated the presence of the proposed (7) "missing" dipeptide sequence (Leu-Arg) at positions 92 and 93. Work in progress strongly suggests the existence of several further errors in the previous sequence for growth hormone. One of these involves residues 130-132, which we find to be Gly-Ser-Pro rather than Pro-Ser-Gly (see Fig. 4).The present report describes sequence studies on lactogen that demonstrate an extremely close homology with the revised growth hormone structure (7). More surprisingly, we also observed unequivocal internal sequence homology between four different regions of the lactogen structure. Examination of the revised ...

The Comments and Addenda section is for short communications which are not o f such urgency as to justify publication in Physical Review Letters and are not appropriate for regular Articles. ft includes only the following types of communications: 11 1 comments on papers previously published in The Physical Review or Physical Review Letters; (2) addenda t o papers previously published in The Physical Review or Physical Review Letters. in which the additional information can be presented without the need for writing a complete article. Manuscripts intended for this section should be accompanied b y a brief abstract for information-retrieval purposes. Accepted manuscripts will follow the same publication schedule as articles in this journal, and galleys will be sent to authors.We show that the existence of a zero-energy (n -1)-body bound state will not produce an infinite number of n -body bound states for n 2 4 We show this in particular for n =4, and sketch the proof for n > 4.

Relaxin is a peptide hormone whose A- and B-chains are derived by posttranslational cleavage from a single 185-amino acid preprorelaxin. Two genes in the human genome (H1 and H2) code for two polypeptides significantly different in amino acid sequence. The full spectrum of biological activities of these two polypeptides has not been examined, but transcription appears to be limited to the H2 relaxin gene in the human corpus luteum. Relaxin is also synthesized by the human decidua, placental trophoblast, and prostate gland; therefore, the expression of the human relaxin genes in these tissues has been examined using the reverse transcription polymerase chain reaction. The mRNA from decidua, placental trophoblast, and prostate was reverse transcribed and then amplified by polymerase chain reaction, using a series of oligonucleotide primers that were specific for but would not distinguish between human H1 and H2 relaxins. Using mRNA from these tissues, two amplified cDNA species were detected, whose identities were confirmed by Southern blots, HpaI and HpaII restriction enzyme analysis, and dideoxy sequencing. We have confirmed that the corpus luteum does not contain detectable H1 relaxin mRNA. However, we demonstrated for the first time relaxin H1 gene expression in the decidua, placental trophoblast, and prostate, and we have also shown that there are marked tissue differences in the relative amounts of expression of the H1 and H2 relaxin mRNA forms. The functional significance is unknown, but if both mRNAs are translated, differential expression of the two genes may result in tissue-specific differences in the production of these relaxins as well as in their binding and actions.

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