THE NUCLEOSOME
THE NUCLEOSOME
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DOI：
10.1038/scientificamerican0281-52
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发表时间：
1981-01-01
影响因子：
3
通讯作者：
KLUG, A
中科院分区：
文献类型：
--
作者：
KORNBERG, RD;KLUG, A
When chromosomes, the carriers of genetic information in high er cells, were first observed through a microscope some 100 years ago, they were seen as dense, rope like bodies moving in two groups toward op posite poles of a dividing cell. The chro mosomes could be followed as each group was incorporated in one of two daughter cells and then enclosed in a membrane-bounded nucleus. Then a strange thing happened: the chromo somes seemed to disappear! They had not, of course, really vanished. They had simply become so thin and diffuse as to be invisible in the microscope. Having b en highly condensed during cell divi sion to facilitate their movement and eq uipartition, the chromosomes had opened up to expose the genetic infor mation needed for the daughter cells' growth and function. The information in chromosomes is divided into the units called genes, many thousands of which are arrayed along the length of the chromosomal material in a typical plant or animal cell. Genes specify the structure of proteins, which in turn carry out cellular functions. These functions differ for different cell types: blood cells, liver cells, brain cells and so on. The sets of proteins each cell type manufactures are therefore different. Yet every cell of an organism contains the same genes. What differs from cell to cell and from time to time is which genes are expressed, or translated into proteins. The necessary selectivity in the expression of genetic information is accompanied by, and may be the con sequence of, selectivity in the unfolding of chromosomes: only the gene regions that are being expressed in a particular cell at a particular time are maximally unfolded and exposed. The great variety of cell types is therefore reflected in an extraordinary diversity of chromosome form and structure. What is the basis of that diversity? The structural flexibility of chromosomes must account not only for selective expression but also for the inclusion, within a cell nucleus less than a hundredth of a millimeter in diameter, of chromosomal material that has a to-
