The complete amino acid sequences and the disulfide arrangements of the two chains of human haptoglobin 1-1 were established. The al and P chains of haptoglobin contain 83 and 245 residues, respectively. Comparison of the primary structure of haptoglobin with that of the chymotrypsinogen family of serine proteases revealed a significant degree of chemical similarity. ITe probability was less than 10-5 that the chemical similarity of the P chain of haptoglobin to the proteases was due to chance. The amino acid sequence of the P chain of haptoglobin is 29-33% identical to bovine trypsin, bovine chymotrypsin, porcine elastase, human thrombin, or human plasmin. Comparison of haptoglobin al chain to activation peptide regions of the zymogens revealed an identity of 25% to the fifth "kringle" region of the activation peptide of plasminogen. The probability was less than 0.014 that this similarity was due to chance. These results strongly indicate haptoglo in to be a homolog of the chymotrypsinogen family of serine proteases. Alignment of the ,Bchain sequence of haptoglobin to the serine proteases is remarkably consistent except for an insertion of 16 residues in the region corresponding to the methionyl loop of the serine proteases. The active-site residues typical of the serine proteases,-histidine-57 and serine-195, are replaced in haptoglobin by lysine and alanine, respectively; however, aspartic acid-102 and the trypsin specificity residue, aspartic acid-189, do occur in haptoglobin. Haptoglobin and the serine proteases represent a striking example of homologous proteins with different biological functions.

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The crystal structure of bovine lens gammaIIIb-crystallin at 2.5 A resolution previously reported was interpreted using a consensus sequence derived from related vertebrate sequences on the assumption that gammaIIIb-crystallin derived from the gammaC-crystallin gene. It has recently been shown that gammaIIIb is a product of the bovine gammaD gene. The structure of gammaIIIb has now been refined with the bovine gammaD sequence using new 1.95 A resolution synchrotron data. The crystallographic R factor was 20.4% for all 33 104 reflection data between 8.0 and 1.95 A measured at 277(1) K. The electron density fully supported the assignment of the gammaD sequence to gammaIIIb. The crystal belongs to space group P2(1)2(1)2(1) with two molecules of molecular mass 20 749 Da in the asymmetric unit in which 219 water molecules were located. The two-domain four-Greek-key motif highly symmetrical protein is very similar in structure to gammaB-crystallin (81% sequence identity). There is a single amino-acid deletion in gammaD in the linker region connecting the two domains. The intermolecular oganization in the crystal lattice is quite different from gammaB as a result of key mutations involving surface residues Leu51, Ile103 and His155. These point mutations will contribute to the intermolecular behaviour of the gamma-crystallins in the eye lens, where they are major components of the densely packed, high refractive index regions of the lens.

Transcription of the etc gene in Bacillus subtilis is activated only after exponentially growing cells enter stationary phase. The promoter of the ctc gene is utilized in vitro by two minor forms of RNA polymerase, Ec37 and Eu32, but not by the most abundant form of RNA polymerase, Er-55. We have used the ctc promoter to direct transcription of the xylE gene on plasmid pLC4 and observed that xylE was expressed only in stationary-phase B. subtilis. We also have constructed a series of homologous plasmids that differ only by