The new study appears in the most recent issue (Oct. 7) of the journal Cell.
The study found that a protein called CPSF73 acts like scissors to cut strands of histone messenger RNA (mRNA) in the cell nucleus. This cutting action produces the mRNA needed to create histone proteins that combine with DNA to form chromosomes.
Like all other proteins, histones are made when a specialized RNA molecule is "read" by ribosomes, the cell's protein factories. The type of RNA, which relays information from the DNA (inside the nucleus) to the ribosome (outside the nucleus), is called messenger RNA.
RNA that is not cut by CPSF73 is destroyed in the nucleus and never becomes messenger RNA, said Dr. William Marzluff, senior author of the study and Kenan distinguished professor of biochemistry and biophysics in UNC's School of Medicine.
"This cutting of histone messenger RNA takes place as growing cells prepare to divide and is absolutely necessary for their eventual division," Marzluff said. Histone proteins help organize and compact within the nucleus the 6 billion nucleotides, or DNA bases, that make up the human genome combinations of "A's," "T's," "G's" and "C's." Without histones, cells cannot survive.
Dr. Zbigniew Dominski, associate professor of biochemistry and biophysics, has been searching for the protein that cuts histone messenger RNA since joining forces with Marzluff 10 years ago. He is the corresponding and lead author of the study.
When RNA is first made from DNA, it is premature and cannot direct the synthesis of its corresponding protein until it is processed into mature messenger RNA, which includes being cut at a specific site, Dominski said.