The heirarchy of packing interactions in chromatin begins with nucleosomes and culminates in mitotic chromosome bands. Lower levels of packing are apparently determined by DNA-histone and histone-histone interactions, but higher levels (such as organization of chromatin into 100 kb topological domains) are probably regulated by non-histone proteins. Our long term goal is to understand the role of non-histone proteins in determining mitotic chromosome architecture. The best candidates for structural non-histone proteins are components of the poorly characterized chromosome scaffold fraction (proteins which remain associated after extraction of 99% of the chromosomal DNA and 95% of the protein). We have recently shown that DNA topoisomerase II is a component of this fraction. We will continue to characterize this and other scaffold components. 1) Antibodies (polyclonal, monoclonal, autoimmune) recognizing specific scaffold antigens will be obtained. These will be used to determine the efficiency of recovery of specific antigens in the scaffold fraction, to localize these antigens in intact chromosomes and whole cells by immunofluorescence and immunoelectron microscopy, to quantitate the antigens across the cell cycle and in non-dividing cells by photometry and immunoprecipitation, and to map the interactions between scaffold components by gradient sedimentation and immunoprecipitation. 2) The role of scaffold proteins in chromosome condensation will be assayed by studying the effect of the antibodies on premature chromosome condensation (induced when mitotic and interphase cells are fused). 3) Highly extended prematurely condensed chromosomes will also be used for structural studies. The folding of the chromatin fiber will be examined using fluorescence microscopy coupled with computer image processing methods. 4) The activity of topoisomerase II in mitotic cells will be examined. We describe an in situ assay for DNA gyrase activity in deproteinized mitotic chromosomes. 5) Finally, we describe a developmental system (chicken erythropoiesis) where scaffold proteins are progessively lost. We will examine the changes in chromatin domain structure which accompany this loss in order to deduce the function of various scaffold components in establishment of nuclear structure. Techniques used will include immunofluorescence, immunoblotting, scanning calorimetry and quantitative fluorimetry (used to measure the size of chromatin domains).

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM030985-07
Application #
3278888
Study Section
Molecular Cytology Study Section (CTY)
Project Start
1983-04-01
Project End
1991-03-31
Budget Start
1989-04-01
Budget End
1990-03-31
Support Year
7
Fiscal Year
1989
Total Cost
Indirect Cost
Name
Johns Hopkins University
Department
Type
Schools of Medicine
DUNS #
045911138
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Saitoh, N; Goldberg, I; Earnshaw, W C (1995) The SMC proteins and the coming of age of the chromosome scaffold hypothesis. Bioessays 17:759-66
Saitoh, N; Goldberg, I G; Wood, E R et al. (1994) ScII: an abundant chromosome scaffold protein is a member of a family of putative ATPases with an unusual predicted tertiary structure. J Cell Biol 127:303-18
Earnshaw, W C; Mackay, A M (1994) Role of nonhistone proteins in the chromosomal events of mitosis. FASEB J 8:947-56
Ma, X; Saitoh, N; Curtis, P J (1993) Purification and characterization of a nuclear DNA-binding factor complex containing topoisomerase II and chromosome scaffold protein 2. J Biol Chem 268:6182-8
Mackay, A M; Eckley, D M; Chue, C et al. (1993) Molecular analysis of the INCENPs (inner centromere proteins): separate domains are required for association with microtubules during interphase and with the central spindle during anaphase. J Cell Biol 123:373-85
Mackay, A M; Earnshaw, W C (1993) The INCENPs: structural and functional analysis of a family of chromosome passenger proteins. Cold Spring Harb Symp Quant Biol 58:697-706
Earnshaw, W C; Bernat, R L (1991) Chromosomal passengers: toward an integrated view of mitosis. Chromosoma 100:139-46
Earnshaw, W C; Rattner, J B (1991) The use of autoantibodies in the study of nuclear and chromosomal organization. Methods Cell Biol 35:135-75
Earnshaw, W C (1991) When is a centromere not a kinetochore? J Cell Sci 99 ( Pt 1):1-4
Earnshaw, W C; Cooke, C A (1991) Analysis of the distribution of the INCENPs throughout mitosis reveals the existence of a pathway of structural changes in the chromosomes during metaphase and early events in cleavage furrow formation. J Cell Sci 98 ( Pt 4):443-61

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