Human cyclin I and genes encoding same

#This invention relates to human cyclin I gene. More specifically, it relates to the amino acid sequence for human cyclin I and a polynucleotide encoding the human cyclin I.

#Cyclin is a general term to describe polypeptides that are subunits controlling the activities of cyclin-dependant protein kinase (Cdk) and eight species of cyclin, namely cyclins A-H, have been documented. Cyclin is known to form a complex with Cdk and to exhibit the capability of intracelluar phosphorylation.

#Also, structural characteristics common in cyclins are that they passes a region called “cyclin box” which comprises about 100 amino acids within portions of their amino acid sequences. It is recognized that the eight species of cyclins hitherto known are provided with a high degree of homology in the amino acid sequences of this cyclin box. Hence, this cyclin box portion is believed to be a step necessary for binding to Cdk and controlling Cdk.

#FIG. 1 shows the base sequence of human cyclin I gene and its corresponding deduced amino acid sequence of human cyclin I protein.

#FIGS. 2A and 2B show a comparison between the amino acid sequence of human cyclin I and the amino acid sequences of other members of the cyclin family. FIG. 2A shows a comparison in the cyclin box (the blackened parts indicate consensus amino acids), and FIG. 2B shows a comparison between human cyclin I and rat cyclin G (the underlined parts indicate the cyclin box).

#FIGS. 3A and 3B are photographs illustrative of localization of human cyclin I mRNA in neuron as determined by the in situ hybridization method using a rat brain section with the aid of an antisense cRNA probe. Both FIG. 3A (as denoted A in the figure) and FIG. 3B (as denoted F in the figure) show a rat brain section centered at its hippocampus and FIG. 3A shows the results obtained using SCG10, while FIG. 3B shows those obtained using cyclin I antisense cRNA as a probe. Here, the parts visible in black are where neurons are concentrated. In the hippocampi (CA1, CA3, and DG), byramidal cells and granulocytes (both neurons) are strongly stained. DG represents “dentate gyrus,” CA3 “Cajail's area 3,” CTX “frontal cortex,” CA1 “Cajail's area 1,” and CP “choroid plexus.”

#As a result of thorough investigations with an aim to achieving the aforementioned objects, the present inventor has extensively screened a gene encoding a protein present in human brain cells and succeeded in isolating a gene encoding cyclin-like polypeptide which has an amino acid sequence with a high degree of homology to the amino acid sequence for the known cyclin box. This gene will be herein referred to as “human cyclin I gene” and the protein encoded by this gene referred to as “human cyclin I.” Further, the present inventor has succeeded in producing the recombinant cyclin I protein in large quantities by incorporating the isolated human cyclin I gene into an expression vector and introducing the expression vector into E. coli cells and have thus accomplished the invention.

#Still further, the present inventor has developed a novel, simple method for selectively detecting neuron by using the thus obtained human cyclin I and a gene thereof. Also, the present inventor has succeeded in preparing anti-human cyclin I sera directed against an antigen resulting from a portion or the whole of the human cyclin protein.

#Furthermore, the present inventor has succeeded in discovering a method to screen cancer cells by using the gene.