(spf) were injected, and those newborn mice were 
found to be corrected from the spf disease traits. 
Analysis of these transgenic mice found the correct- 
ing transgene to be expressed in the small bowel, 
not in the liver. These studies suggest delivery of 
correcting genes to small bowel may be a more fac- 
ile method of gene correcting efforts than that di- 
rected to correction in liver. Viral vectors are now 
developed toward that goal. 
V Adenosine Deaminase. 
Long-term expression of human adenosine deam- 
inase (ADA) has been obtained in mice via the infec- 
tion of hematopoietic stem cells with an N2-deriva- 
tive retroviral vector (see the report of Dr. John W 
Belmont). An efficient system of retroviral gene 
transfer of ADA in human hematopoietic cells is 
now being developed. Five to 20% of unselected 
human colony-forming progenitors contained an 
integrated copy(ies) of the provirus after infection 
with virus-containing supernatants. Infected bone 
marrow cells (BMCs) were detected for up to seven 
weeks in long-term cultures. Transduced ADA ex- 
pression was also detectable after infection of BMCs 
from two ADA-deficient patients. In parallel, modi- 
fied vectors have been constructed for high-level 
expression in T and B cells. These produce high ti- 
ters of virus and successfully transduce human ADA 
in target cell lines. Their potential tissue-specific ex- 
pression is being evaluated in cell lines and in long- 
term reconstituted animals. These studies provide a 
rational scientific basis for attempts to correct ADA 
immunodeficiency in humans. 
VI. Xq28 Disease Genes. 
Cloning and characterization of the terminal end 
of the long arm of the human X chromosome has 
the potential for simultaneous identification of 25 
disease genes. Yeast artificial chromosome (yAC) li- 
braries have been prepared from somatic cell hy- 
brid lines containing either an intact X chromo- 
some (4.12) orXq24-qter (X3000-11), and human 
PUBLICATIONS 
clones have been identified. Over 200 human 
clones have been isolated from the X3000-11 li- 
brary, and 40 have been localized to specific X re- 
gions. One of these YAC clones appears to contain 
the gene defective in the oculocerebrorenal syn- 
drome of Lowe. The 4.12 library has over 150 
human clones, and 20 have been localized to spe- 
cific X regions. A new method of preparing human- 
specific DNA from the YAC (Alu PCR) uses PCR 
amplification of human DNA specifically with oligo- 
nucleotide primers directed to the human Alu re- 
petitive sequence. This method allows isolation 
and characterization of human DNAs from somatic 
cell hybrids, preparation of insert sequences with- 
out subcloning, and direct isolation of identifying 
tag sequences from the YAC 5' and 3' sequences. A 
means of identifying expressed genes in a chromo- 
somal region has been developed using ro- 
dent/human somatic cell hybrids containing small 
regions of the human X by the direct isolation of 
human cDNA from heterogeneous nuclear RNA. 
VII. Peptide Chain Termination. 
The isolation and characterization of a mamma- 
lian release factor (RF) cDNA has been the focus of 
recent efforts in protein synthesis. The rabbit RF 
cDNA has been fully characterized and expressed as 
a protein in bacteria. The in vitro synthesized RF 
has stop codon specificity and requires GTP, all fea- 
tures of a mammalian RF. Sequence comparisons 
find the RF to be similar to tryptophanyl-tRNA syn- 
thetases from bacteria and yeast, suggesting an evo- 
lutionary relationship between mammalian RFs and 
the AA-tRNA synthetases. The characterization of 
the mouse RF gene for function domains is under 
way. Structure-function comparisons of RF genes 
from a variety of bacterial species and mammalian 
mitochondria are proceeding. 
Dr. Caskey is also Professor at the Institute for 
Molecular Genetics and Professor of Medicine, Bio- 
chemistry, and Cell Biology at Baylor College of 
Medicine. 
Books and Chapters of Books 
Caskey, C.T 1988. Prospects for gene therapy. In Textbook of Internal Medicine (Kelley WN., DeVita, VT, Du- 
Pont, H.L., Harris, E.D., Hazzard, WR., Holmes, E.W, Hudson, L.D., Humes, H.D., Paty D.W, Watanabe, 
A.M., and Yamada, T, Eds.). Philadelphia, PA: JB Lippincott, pp 2349-2350. 
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