The Adenine Pathway in yeast

Yeast

Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...

 is a seven step pathway converting P-ribosyl-PP to adenine

Adenine

Adenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and protein synthesis, as a chemical component of DNA...

. This product is then either integrated into DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

, RNA

RNA

Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

, or a ribose diphosphate molecule ADP

Adenosine diphosphate

Adenosine diphosphate, abbreviated ADP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside adenosine. ADP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase adenine....

, the precursor of ATP

Adenosine triphosphate

Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...

, an essential intermediate storage molecule for most cellular processes.

Mechanism

The ADE series of enzymes converts the most precursory molecule, P-ribosyl-PP, into adenine by this seven step process. AIR synthetase is ADE 6, and essentially is what closes the five membered ring to form the purine base.

Molecular precursor	Enzyme
P-ribosyl-PP	none (original precursor)
P-ribosylamine	ADE4
P-ribosylglycinamide	ADE5
P-ribosylformyl glycinamide	ADE8
P-ribosylformyl glycinamidine	ADE6
P-ribosylamino imidazole (AIR)	ADE7
P-ribosylamino imidazolecarboxylate (CAIR)	ADE2
P-ribosylsuccino carboxamide aminoimidazole (SAICAIR)	ADE1
Adenine

Mutation

Deletion or mutation in Ade2 results in the accumulation of a red precursor in the cells. Colonies formed by such cells would therefore be red.