Molecular Arrangement and Evolution of Heterochromatic Dna

INTRODUCTION . .... . . . ... ... .. . .... . ... . . . . . . . . .. . ... . . . . . . . ... . . . . ... . . . ... . ..... . . . . . . ... . ..... .. . . . . . ... ... ... ....... 121 INTERSPECIFIC VARIATION OF HIGHLY REPEATED DNA SEQUENCES . .... ... ... . . .. ....... . . . ... ... ... ... ......... . . . . . ... ... . ... . ..... . ...... 122 MECHANISMS OF EVOLUTION OF TANDEMLY REPEATED REGIONS .. ... . . ... . . . . . . . .. . . . .... . ..... ... ... . . . ... ... .. . ..... .. . ......... ... .... ... ... 123 SEQUENCE DIVERGENCE WITHIN SATELLITE DNAS . . 125 Random Variation of Restriction Recognition Sites 125 Regular Alteration of Satellite Repeat Units ........ 126 Uniform Variation of Repeat Units in Local Regions 127 Uniform Sequence Variation Near the Ends of Tandemly Repeated Arrays ..... ..... 128 Divergence of Tandem Repeats by Long Insertions and Deletions 129 MULTIPLE PERIODICITIES IN SATELLITE DNA .. . . . .. . . ...... ... . ..... . . . 130 Homologies Within Satellite Repeat Units 130 Homologies Between Diff erent Satellite Repeat Units 132 Relationships Among Simple-Sequence Satellites 133 ARRANGEMENT AND FUNCTION OF SATELLITE DNA IN HETEROCHROMATIN .. . . .. . ... ... ..... . . ... . . . . . ... ... . ......... . . ... .... ... .... ... . .. . 133 Localization of Highly Repeated Satellite DNAs 133 Functions of Heterochromatin 136 Proteins Associated with Satellite DNA 137 CONCLUSIONS... . . . . . . . . . .... . . . ... ... . . ..... . . . ... . ........ . . . . . ... . .... 139