Two 19-base-long oligonucleotides were synthesized, one complementary to the normal human j-globin gene (pA) and one complementary to the sickle cell (-globin gene (PS).The nonadecanucleotides were radioactively labeled and used as probes in DNA hybridization. Under appropriate hybridization conditions, these probes can be used to distinguish the pJA gene from the 3ss allele. The DNA from individuals homozygous for the normal fi-globin gene (fApA) only hybridized with the plA specific probe; the DNA from those homozygous for the sickle cell ,3-globin gene ((s.(s) only hybridized with the SsS specific probe. The DNA from heterozygous individuals (pATS) hybridized with both probes. This allele-specific hybridization behavior of oligonucleotides provides a general method for diagnosis of any genetic disease which involves a point mutation in the DNA sequence of a single-copy gene.

The rat serum albumin gene has been isolated from a recombinant library containing the entire rat genome cloned in the X phage Charon 4A. Preliminary R-loop and restriction analysis has revealed that this gene is split into at least 14 fragments (exons) by 13 intervening sequences (introns), and that it occupies a minimum of 14.5 kilobases of genomic DNA.Recent advances in recombinant DNA technology have made it possible to obtain virtually any desired single-copy genomic sequence in cloned form, provided an appropriate probe is available. We have used these techniques to isolate the rat serum albumin gene. Serum albumin synthesis is one of the major characteristics of vertebrate liver. Observation of the activity and state of this gene during development and in adult tissues should be informative as to the process of terminal differentiation. Albumin synthesis is essentially constitutive, but does respond significantly to a variety of stimuli (1). It is also expressed to variable extents in different hepatoma cell lines (2). The availability of cloned albumin genomic DNA will greatly facilitate the study of this variable expression, particularly at the level of transcript processing.Determination of the sequence organization of the albumin gene is also of interest, especially with regard to the disposition of repetitive elements and intervening sequences. Although regulatory (3) and evolutionary (4) significance has been postulated, the functional role, if any, of these striking features of eukaryotic genomes remains unknown. The comparative studies that will be possible as other genes are extracted from the rat and related species can be expected to provide considerable insight into this fascinating problem. MATERIALS AND METHODSRat Genome Library. High molecular weight liver DNA was extracted from an adult male Sprague-Dawley rat (Simonsen Labs, Gilroy, CA) by the method of Blin and Stafford (5) and aliquots were digested with EcoRI (Boehringer Mannheim) under conditions adjusted to cleave either one-third or one-fifth of the EcoRI sites in an equivalent amount of bacteriophage X DNA. The fragments resulting from this partial digestion were sedimented through a 10-30% sucrose gradient; the material between 10 and 20 kilobases (kb) was recovered by ethanol precipitation. A sample of this rat DNA (2.5 ,g) was ligated with 8.5 ,ig of a preparation of Charon 4A "cloning fragments" (6, 7). This recombinant DNA was packaged in vitro by using extracts from defective X lysogens provided by N. Sternberg (6). The method used was that of Hohn and Murray (8). Approximately 2,000,000 independent clones were obtained. The library was amplified 100,000-fold by subconfluent plating on Escherichia coli strain DP5OSupF (9).cDNA Clones. cDNA was synthesized from purified albumin mRNA as described (10). This cDNA contained a small amount of full-length material and had a number average size of approximately 1000 nucleotides. It was rendered double-stranded by sequential treatment with E. coli DNA polymerase I and S1 nuc...

or deleted HBD (HBD-) at levels similar to those of wild-type NCAM. Mutant NCAM polypeptides purified from transfected cell lines have substantially reduced binding to heparin and fail to promote chick retinal cell attachment. Furthermore, whereas a synthetic peptide that contains both basic amino acid clusters inhibits retinal-cell adhesion to NCAMcoated dishes, synthetic peptides in which either one of the two basic regions is altered to contain only neutral amino acids do not inhibit this adhesion. These results confirm that this region of the NCAM polypeptide does indeed mediate not only the large majority of NCAM's affinity for heparin but also a significant portion of the cell-adhesionmediating capability of NCAM.t Corresponding author.

The major membrane-associated or transmembrane isoforms of the neural cell adhesion molecule (NCAM) are generated by alternative splicing at the 3' end of the mRNA. Further diversity in NCAM structure is observed in the extraceliular region of the polypeptide, where the insertion of additional amino acid residues can result from alternative splicing events occurring at the exon 7-exon 8 and exon 12-exon 13 junctions. Here we report the characterization of tissue-specific patterns of alternative splicing at the exon 12-exon 13 junction by using the polymerase chain reaction. Nine alternatively spliced sequences in rat heart between exon 12 and exon 13 were identified. Each sequence consisted of different combinations of the three small exons (15, 48, and 42 bp in length) and the AAG triplet that make up MSD1, the 108-bp muscle-specific sequence found in human skeletal muscle NCAM (G. Dickson, H. J. Gower, C. H. Barton, H. M. Prentice, V. L. Elsom, S. E. Moore, R. D. Cox, C. Quinn, W. Putt, and F. S. Walsh, Cell 50:1119-1130. Although the rat equivalent of MSD1 (designated 15'48'42+3+) was detected in all ages of heart examined, it was only one of four or five major splice combinations at any given age. The only alternatively spliced sequence found in the exon 7-exon 8 junction of heart NCAM mRNA was the 30-bp variable alternatively spliced exon previously identified in rat brain. Twenty-seven NCAM forms with distinct sequences were found by analysis of individual NCAM transcripts from postnatal day 1 heart tissue for alternative splicing at the exon 7-exon 8 junction, the exon 12-exon 13 junction and the 3' end. Several combinations of splicing patterns in these three different regions of the gene appeared to be preferentially expressed. The observation that the expression of alternatively spliced forms of NCAM is developmentally regulated suggests a role for NCAM diversity in cardiac development.Regulation of gene expression can occur at the transcriptional, posttranscriptional, translational, and posttranslational levels. One control mechanism that occurs posttranscriptionally in eukaryotes is alternative splicing.

with the hypothesis that the mutation was not a random event but may be the result of a block transfer of information by a copy mechanism analogous to gene conversion. As the sequence analysis of the coding region for the first 273 amino acid residues shows identity between parent and mutant except for the seven nucleotide changes, all variant-parent functional. differences must depend only on the cluster of three amino acid differences in the second domain of the Kb glycoprotein. Studies on the spontaneously occurring H-2 major histocompatibility complex (MHC) variants have permitted a unique approach to the analysis of structure-function relationships of class I genes. The variant mouse sublines were discovered and isolated