grew, A.L., Herrera, C.A., Hammond, H.A., Cas- 
key, ex., Zoghbi, H.Y., and Ledbetter, D.H. 
1991 . Linkage of the gene for an X-linked mental 
retardation disorder to a hypervariable (AGAT)„ 
repeat motif within the human hypoxanthine 
phosphoribosyltransferase (HPRT) locus (Xq26). 
Am J Hum Genet 49:\5\2-\5l9 . 
Jones, S.N. , Jones, P.G., Ibarguen, H., Caskey, C.T., 
and Craigen, W.J. 1991. Induction of the Cypla- 1 
dioxin-responsive enhancer in transgenic mice. 
Nucleic Acids Res 19:6547-6551. 
Kilimann, M.W., Pizzuti, A., Grompe, M., and Cas- 
key, C.T. 1992. Point mutations and polymor- 
phisms in the human dystrophin gene identified 
in genomic DNA sequences amplified by multi- 
plex PGR. Hum Genet 89:253-258. 
Moore, K.A., Scarpa, M., Kooyer, S., Utter, A., Cas- 
key, ex., and Belmont, J.W. 1991. Evaluation 
of lymphoid-specific enhancer addition or substi- 
tution in a basic retrovirus vector. Hum Gene 
Ther 2-307-515. 
Pettigrew, A.L., Greenberg, F., Caskey, C.X., and 
Ledbetter, D.H. 1991. Greig syndrome associated 
with an interstitial deletion of 7p: confirmation of 
the localization of Greig syndrome to 7pl 3. Hum 
Genet 87:452-456. 
Pizzuti, A., Pieretti, M., Fenwick, R.G., Gibbs, R.A., 
and Caskey, C.X. 1992. A transposon-like ele- 
ment in the deletion-prone region of the dystro- 
phin gene. Genomics 13:594-600. 
Riggins, G.J., Sherman, S.L., Oostra, B.A., Sutcliffe, 
J.S., Feitell, D., Nelson, D.L., van Oost, B.A., 
Smits, A.P.T., Ramos, F.J., Pfendner, E., Kuhl, 
D.P.A., Caskey, C.X., and Warren, S.X. 1992. 
Characterization of a highly polymorphic dinucle- 
otide repeat 1 50 kb proximal to the fragile X site. 
Am J Med Genet 43:237-243. 
Rossiter, B.J.F., Stirpe, N.S., and Caskey, C.X. 1992. 
Report of the MDA Gene Therapy Conference, 
Tucson, Arizona, September 27-28, 1991. Neu- 
rology 42:1413-1418. 
Sutcliffe, J.S., Zhang, F., Caskey, C.X., Nelson, 
D.L., and Warren, S.X. 1992. PGR amplification 
and analysis of yeast artificial chromosomes. Ge- 
nomics 13:1303-1306. 
Taylor, L.D., Krizman, D.B., Jankovic, J., Hayani, A., 
Steuber, P.C., Greenberg, F., Fenwick, R.G., and 
Caskey, C.X. 1991. 9p monosomy in a patient 
with Gilles de la Tourette's syndrome. Neurology 
41:1513-1515. 
Wu, X., Muzny, D.M., Lee, C.C., and Caskey, C.X. 
1992. Two independent mutational events in the 
loss of urate oxidase during hominoid evolution./ 
Mol Evol 54:78-84. 
RNA CAXALYSIS AND XHE SXRUCXURE OF CHROMOSOME ENDS 
XhomasR. Cech, Ph.D., Investigator 
One goal of the research in Dr. Cech's laboratory 
is to understand how RNA molecules catalyze bio- 
chemical reactions. RNA-mediated catalysis is in- 
volved in many RNA-processing reactions, which are 
essential steps in gene expression, and RNA catalysis 
appears to be central to protein synthesis on ribo- 
somes. Dr. Cech's research group continues to use 
the self-splicing intron from the Tetrahymena ther- 
mophila rRNA precursor as a model system for study- 
ing structure-function relationships in RNA cataly- 
sis, although other ribozymes (catalytic RNA 
molecules) are also being investigated. In the very 
different area of chromosome structure, Dr. Cech 
and his colleagues are studying DNA-protein inter- 
actions at telomeres, the natural ends of linear chro- 
mosomes. 
Xertiary Structure Around the 
Guanosine-binding Site 
of the Tetrahymena Ribozyme 
A cleavage reagent designed to bind to the active 
site of the ribozyme was synthesized by derivatizing 
guanosine, normally a substrate in the RNA- 
catalyzed reaction, with a metal chelator. This re- 
agent, when complexed with iron(II), cleaved the 
ribozyme in five regions. One region at A207 is far 
from the guanosine-binding site in the primary and 
secondary structures, and therefore provides a con- 
straint for the higher-order folding of the ribozyme. 
This cleavage site provides physical evidence for a 
major feature of the three-dimensional structure 
model of Drs. Francois Michel and Eric Westhof. 
This sort of targeting of a reactive species to a spe- 
GENETICS 167 
