In recent years, members of the protein kinase family have been discovered at an accelerated pace. Most were first described, not through the traditional biochemical approach of protein purification and enzyme assay, but as putative protein kinase amino acid sequences deduced from the nucleotide sequences of molecularly cloned genes or complementary DNAs. Phylogenetic mapping of the conserved protein kinase catalytic domains can serve as a useful first step in the functional characterization of these newly identified family members.

http://science.sciencemag.org/content/sci/241/4861/42.full.pdf

The protein kinase family: conserved features and deduced phylogeny of the catalytic domains.

Src homology (SH) regions 2 and 3 are noncatalytic domains that are conserved among a series of cytoplasmic signaling proteins regulated by receptor protein-tyrosine kinases, including phospholipase C-gamma, Ras GTPase (guanosine triphosphatase)-activating protein, and Src-like tyrosine kinases. The SH2 domains of these signaling proteins bind tyrosine phosphorylated polypeptides, implicated in normal signaling and cellular transformation. Tyrosine phosphorylation acts as a switch to induce the binding of SH2 domains, thereby mediating the formation of heteromeric protein complexes at or near the plasma membrane. The formation of these complexes is likely to control the activation of signal transduction pathways by tyrosine kinases. The SH3 domain is a distinct motif that, together with SH2, may modulate interactions with the cytoskeleton and membrane. Some signaling and transforming proteins contain SH2 and SH3 domains unattached to any known catalytic element. These noncatalytic proteins may serve as adaptors to link tyrosine kinases to specific target proteins. These observations suggest that SH2 and SH3 domains participate in the control of intracellular responses to growth factor stimulation.

https://science.sciencemag.org/content/sci/252/5006/668.full.pdf

SH2 and SH3 Domains: Elements that Control Interactions of Cytoplasmic Signaling Proteins

Allelic deletions involving chromosome 18q occur in more than 70 percent of colorectal cancers. Such deletions are thought to signal the existence of a tumor suppressor gene in the affected region, but until now a candidate suppressor gene on this chromosomal arm had not been identified. A contiguous stretch of DNA comprising 370 kilobase pairs (kb) has now been cloned from a region of chromosome 18q suspected to reside near this gene. Potential exons in the 370-kb region were defined by human-rodent sequence identities, and the expression of potential exons was assessed by an "exon-connection" strategy based on the polymerase chain reaction. Expressed exons were used as probes for cDNA screening to obtain clones that encoded a portion of a gene termed DCC; this cDNA was encoded by at least eight exons within the 370-kb genomic region. The predicted amino acid sequence of the cDNA specified a protein with sequence similarity to neural cell adhesion molecules and other related cell surface glycoproteins. While the DCC gene was expressed in most normal tissues, including colonic mucosa, its expression was greatly reduced or absent in most colorectal carcinomas tested. Somatic mutations within the DCC gene observed in colorectal cancers included a homozygous deletion of the 5' end of the gene, a point mutation within one of the introns, and ten examples of DNA insertions within a 0.17-kb fragment immediately downstream of one of the exons. The DCC gene may play a role in the pathogenesis of human colorectal neoplasia, perhaps through alteration of the normal cell-cell interactions controlling growth.

https://science.sciencemag.org/content/sci/247/4938/49.full.pdf

Identification of a chromosome 18q gene that is altered in colorectal cancers

Five structural features in mRNAs have been found to contribute to the fidelity and efficiency of initiation by eukaryotic ribosomes. Scrutiny of vertebrate cDNA sequences in light of these criteria reveals a set of transcripts--encoding oncoproteins, growth factors, transcription factors, and other regulatory proteins--that seem designed to be translated poorly. Thus, throttling at the level of translation may be a critical component of gene regulation in vertebrates. An alternative interpretation is that some (perhaps many) cDNAs with encumbered 5' noncoding sequences represent mRNA precursors, which would imply extensive regulation at a posttranscriptional step that precedes translation.

https://rupress.org/jcb/article-pdf/115/4/887/1062268/887.pdf

An analysis of vertebrate mRNA sequences: intimations of translational control.

https://www.cell.com/cell/pdf/0092-8674(88)90053-0.pdf

The CD4 and CD8 T cell surface antigens are associated with the internal membrane tyrosine-protein kinase p56lck

With v-yes DNA as the probe, a human cDNA library made from placental RNA was screened under relaxed conditions, and DNA clones derived from a novel genetic locus, termed lyn, were obtained. Nucleotide sequencing revealed that lyn could encode a novel tyrosine kinase that was very similar to mouse T-lymphocyte-specific tyrosine kinase p56lck and the v-yes protein as well as to the gene products of v-fgr and v-src. Northern hybridization analysis revealed that a 3.2-kilobase lyn mRNA was expressed in a variety of tissues of the human fetus. The pattern of lyn mRNA expression was different from those of related genes, such as yes and syn. Hybridization analysis of DNA from sorted chromosomes showed that the lyn gene is located on human chromosome 8 q13-qter.

The yes-related cellular gene lyn encodes a possible tyrosine kinase similar to p56lck.

An src/yes-related novel gene named syn (SYN in human gene nomenclature) has been identified in the human genome on chromosome 6 and characterized by molecular cloning. Nucleotide sequence analysis of cDNA clones showed that the c-syn gene could encode a protein-tyrosine kinase that is very similar in primary structure to the v-yes and human c-src proteins. A 2.8-kilobase transcript of the c-syn gene, which differs in size from those of the c-yes, c-src, and c-fgr genes, was observed in various cell types. These results show that syn is a new member of the tyrosine kinase oncogene family.

yes-related protooncogene, syn, belongs to the protein-tyrosine kinase family

Three c-yes cDNA clones were obtained from poly(A)+ RNA of human embryo fibroblasts. Sequence analysis of the clones showed that they contained inserts corresponding to nearly full-length human c-yes mRNA, which could encode a polypeptide of 543 amino acids with a relative molecular weight (Mr) of 60,801. The predicted amino acid sequence of the protein has no apparent membrane-spanning region or suspected ligand binding domain and closely resembles pp60c-src. Comparison of the sequences of c-yes and v-yes revealed that the v-yes gene contains most of the c-yes coding sequence except the region encoding its extreme carboxyl terminus. The region missing from the v-yes protein is the part that is highly conserved in cellular gene products of the protein-tyrosine kinase family.

Characterization of cDNA clones for the human c-yes gene.

Analysis of DNA from human embryo fibroblasts showed that ten Eco RI fragments were hybridizable with the Yamaguchi sarcoma virus oncogene (v-yes). Four of the Eco RI fragments were assigned to chromosome 18 and one to chromosome 6. There was evidence for multiple copies of yes-related genes in the human genome; however, only a single RNA species, 4.8 kilobases in length, was related to yes in various cells.

Jun Sukegawa

Papers

The yes-related cellular gene lyn encodes a possible tyrosine kinase similar to p56lck.

yes-related protooncogene, syn, belongs to the protein-tyrosine kinase family

Characterization of cDNA clones for the human c-yes gene.

Location of the c-yes Gene on the Human Chromosome and its Expression in Various Tissues

Human liver type pyruvate kinase: cDNA cloning and chromosomal assignment.