Chromosomal mapping of three human LAMMER protein-kinase-encoding genes.

The eukaryotic LAMMER protein kinase family is encoded by at least three loci in the human genome, designated CLK1, 2, and 3. We have mapped these loci to 2q33, 1q21, and 15q24, respectively, by fluorescent in situ hybridization. Additionally, a CLK2 pseudo-gene has been located to 7p15-21.

Cell-specific organization of the 5S ribosomal RNA gene cluster DNA loop domains in spermatozoa and somatic cells.

DNA in eucaryotic cells is organized into loop domains, ranging in size from 25 to 100 kb, that are attached at their bases to the structural component of the nucleus termed the nuclear matrix. These DNA loop domains have been shown to be important in the regulation of both DNA replication and RNA transcription. In this study we have compared the structural organization of the DNA loop domains of the 5S rRNA gene cluster in sperm, liver, and brain nuclei in the Syrian golden hamster. The individual loop domains were visualized by fluorescent in situ hybridization to protamine (sperm)- and histone (somatic)-depleted nuclei, termed nuclear matrix halo preparations. We found that in sperm nuclei, the 5S rRNA gene cluster was organized into three small loop domains that were approximately 48 kb each. In both types of somatic cell nuclei examined, the 5S rRNA gene cluster was organized into a single, much larger loop domain that was up to 480 kb in length. The data suggest that at least some of the compaction that sperm DNA undergoes during spermiogenesis is mediated by the nuclear matrix independent of protamine binding. Additionally, this sperm-specific DNA organization may be involved in the specific patterns of DNA replication and transcription of the paternal genome in the embryo.

Identification and chromosomal mapping of a receptor tyrosine kinase with a putative phospholipid binding sequence in its ectodomain.

We have cloned a novel receptor tyrosine kinase that has an unusual ectodomain. The extracellular sequence consists of 416 amino acids and has none of the structural motifs that have been found in other receptor tyrosine kinases. The 150 amino acids in the amino terminus of the receptor is homologous to a putative phospholipid-binding sequence that is found also in other cell adhesion molecules such as the neuronal A5 antigen and coagulation factors V and VIII. The kinase domain has a short cytoplasmic tail and contains a short insert between subdomains I and II. The structure of this receptor kinase suggests that it belongs to a new family of receptors involved in cell-cell interactions. The cell adhesion kinase (Cak) is expressed at low levels in most adult tissues and expression is highest in the brain and lung. Using fluorescence in situ hybridization and interspecific backcross mapping, the Cak gene was localized to human chromosome 6 and mouse chromosome 17.