Lambda does not uniquely occupy its ecological niche. A variety of both close and distant relatives of lambda are known. The near relatives all possess the same sticky ends of the chromosome and are of almost the same size and genetic structure as lambda. Some possess the same immunity as lambda, which means that they cannot grow in lambda lysogens, but others possess different immunities and can grow in lambda lysogens (Table 1). That is, they are heteroimmune. Remark ably, lambda relatives can form recombinants between one another to form hybrids. DNA heteroduplexes between them show that their genes tend to be either closely homologous or quite dissimilar. It is as though nature possesses a few fundamental lambda-type phage and can inter change their parts to produce the large number of different lambdoid phage that are observed.

Table1. Properties of a Number of Lambdoid Phage

A study of the similarities and differences between lambda’s relatives has been fruitful in understanding lambda. Phage 21, φ80, and 434 have been particularly useful in the research on phage lambda. They have highlighted the crucial invariants of lambdoid growth and regulation. Recombinant hybrids have also been constructed between lambda and both 21 and 434 (Fig. 1). These were constructed so as to retain the immunity of the heteroimmune phage but to contain as much of the rest of lambda as possible. These lambda hybrids are called λimm⁴³⁴, or λi⁴³⁴, and λi²¹. They permit recombination and complementation studies that otherwise would be impossible because of the existence of immunity.

Fig1. The regions of the phage λ genome that are replaced by segments of 21 and 434 in hybrid λimm²¹ and λimm⁴³⁴.

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مواضيع ذات صلة

Genotoxicity Through Potential Off-target Nuclease - Induced Double - Strand Breaks

A Broad Range of Genomic Changes by Homologous Recombination–Mediated Genome Editing

Early Transcription of Genes N and Cro

The Genetic Structure of Lambda

The Physical Structure of Lambda

Other Attenuated Systems: Operons, Bacillus subtilis and HIV

Coupling Translation to Termination

trp Multiple Secondary Structures in trp Leader RNA

Early Explorations of the Hypersynthesis

The Serendipitous Discovery of trp Enzyme Hypersynthesis

Rapid Induction Capabilities of the trp Operon

The Aromatic Amino Acid Synthetic Pathway and its Regulation