Current controversies over metaphase chromosome architecture arise from the extreme chromatin packing density in the chromatid which precludes observation of individual chromatin fibers over significant distances. Also, little is known concerning cellular mechanisms controlling chromosome condensation at mitosis. I will approach these problems by analysing the controlled condensation of minute chromosomes in vivo. Double minutes are tiny chromosomes found only in tumor-derived cell lines. They apparently contain amplifications of cellular DNA sequences. Normal chicken cells also contain minute chromosomes. Chromosome condensation will be induced by fusing interphase cells containing minute chromosomes with metaphase-arrested HeLa cells. This induces premature chromosome condensation in the interphase nuclei. the process resembles normal prophase, but the final degree of condensation varies greatly as a function of the interphase cell cycle position. I will produce samples for electron microscope analysis covering a wide range of condensation. This range, coupled with the tiny size of the minute chromosomes should permit great improvement in the visualization of individual chromain fiber paths. Also, since minute and normal chromosomes are readily separable, the approach should permit identification of protein factors involved in the premature condensation. In both microscope and biochemical analysis, particular attention will be given to components of the non-histone protein scaffold, a substructure thought to be involved in maintaining the compact structure of mitotic chromosomes. The electron microscope techniques I will use feature modified Miller spreading procedures, involving sedimentation of chromosomes onto carbon-coated microscope grids. These procedures have already permitted me to improve visualization of substructural detail in normal chromosomes and residual scaffolds. I will also exploit a new ultra-quick-freeze: deep-etch method which virtually eliminates two major problems of chromosome microscopy; structural distortion during sample preparation, and superposition of image detail from thick specimens.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM030985-03
Application #
3278885
Study Section
Molecular Biology Study Section (MBY)
Project Start
1983-04-01
Project End
1986-03-31
Budget Start
1985-04-01
Budget End
1986-03-31
Support Year
3
Fiscal Year
1985
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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