Cloning heterologous genes: problems and approaches.

Model fungi such as Neurospora crassa, Aspergillus niger, and Saccharomyces cerevisiae have provided a wealth of genetic information and are currently the object of cooperative genome sequencing projects. Many agriculturally and medically economic important pathogenic fungi, however, are less well characterized, which makes it difficult to study their genes and gene products. Gene sequences from model fungi offer a unique opportunity to clone cognate genes from pathogenic counterparts. In this review, we propose three basic strategies for cloning such genes: Functional complementation, sequence similarity, and genetic linkage. These strategies involve Southern hybridization, cloning, library screening, genetic complementation, and the polymerase chain reaction. We review the major problems encountered using these strategies and outline useful solutions to these difficulties.