Molecular Genetics

Facts

Molecular genetic methods are used to identify origin-containing DNA sequences.

A circular DNA bearing the LEU2 selectable gene transforms Saccharomyces cerevisiae leu2 cell to leucine independence with very low efficiency. Random fragments of S. cerevisiae DNA were ligated into the circular DNA. The products were used to transform leu2 yeast cells. Many colonies were obtained. Circular DNA isolated from the colonies transformed the leu2 cells to leucine independence with high efficiency. Deletion analysis of the inserts in the high efficiency transforming DNAs suggests that the region of the inserts responsible for the high efficiency is limited to about 50 bp. These sequences are called ARS (autonomously replicating sequences). Comparison of the essential sequences from several such DNAs revealed that they all contain an 11 bp sequence (ARS consensus) or a sequence closely related to it. Random fragments of DNA from other organisms when cloned into the yeast circular DNA can also function as ARS sequences.

Interpretations

• An ARS consists of an essential 11 bp sequence and two or three auxilliary sequences.
  
• Sequences of other organisms that function as ARS in yeast are not necessarily origins in the species from which they were derived.

Further information

• Mammalian origins of replication differ significantly from those in Saccharomyces.
• There are other methods of identifying origins.

This is page 1323 of Molecular Genetics by Ulrich Melcher, © 1997, 1998, 1999