both been crystalli2ed. The crystals of the latter are 
superior in quality and are currently the subject of 
structural analysis. The crystals show the symmetry 
of the orthorhombic space group P2^2^2^, with the 
following unit cell dimensions: a = 74.59 A, b = 
88.78 A, and c = 40.11 A. There is a single mole- 
cule per asymmetric unit with a of 2.23 A^/Da. 
Native data have been collected on a multiwire area 
o 
detector to a resolution of 2.4 A. Data (including 
Friedel pairs) have also been collected on a deriva- 
tive crystal to 2.4 A. Four sites of heavy metal bind- 
ing have been located from Patterson and residual 
maps. Due to the expected similarity of the ribose- 
binding protein to the galactose/glucose receptor, a 
single derivative may prove sufficient for a structure 
solution, combining heavy atom phases with mo- 
lecular replacement and/or solvent-flattening meth- 
ods. Because the ribose receptor protein has been 
crystallized in the absence of bound ligand, this 
structure should give a picture of the more open 
state expected in this case. 
The dipeptide-binding protein is the primary re- 
ceptor for both chemotaxis toward, and transport 
of, dipeptides. This protein is interesting partly be- 
cause of the possibility of developing suicide at- 
tractants in the form of antibiotics. In addition, the 
fact that a large variety of dipeptides are bound by 
this protein poses interesting problems concerning 
how the strength of ligand binding is maintained in 
a protein that most likely acts by closing down and 
burying its ligand. A method of purifying large 
quantities of the E. colt dipeptide receptor has 
been worked out, and this protein is currently the 
subject of crystallization studies. Small, apparently 
single, crystals have been obtained and are being 
studied by x-ray methods. 
IV E. coli Leader Peptidase. 
The leader peptidase of E. coli has been well de- 
scribed as the agent by which signal sequences are 
removed from proteins as they are transported 
across membranes. Dr. Mowbray and her col- 
leagues have developed a reliable method of large- 
scale purification with apparently complete inhibi- 
tion of proteolytic degradation (a serious problem 
previously). The crystallization and successful 
structure solution of this protein would add valu- 
able data about this key step of the transport event. 
Dr. Mowbray is also Assistant Professor in the De- 
partments of Biochemistry and Pharmacology at the 
University of Texas Southwestern Medical Center at 
Dallas. 
590 
