[1] Spf is found in gammaproteobacteria and the majority of experimental work on Spot42 has been performed in Escherichia coli [2][3] and recently in Aliivibrio salmonicida.

[4] In the cell Spot42 plays essential roles as a regulator in carbohydrate metabolism and uptake, and its expression is activated by glucose, and inhibited by the cAMP-CRP complex.

It was discovered by polyacrylamide gel electrophoresis and 2-D fingerprinting in an attempt to study the accumulation of small RNAs in E. coli during amino acid starvation.

[7] Later experiments showed that over-expression of Spot42 (~10 fold increase) resulted in impaired growth and lowered ability to adapt to shifts to richer media.

[11] The natural distribution of the spf gene is restricted to 5 orders of gammaproteobacteria; Enterobacteriales, Aeromonadales, Vibrionales, Alteromonadales, Chromatiales.

[12] The spf gene is highly conserved in Escherichia, Shigella, Klebsiella, Salmonella, Yersinia genera within the family Enterobacteriaceae.

Bækkedal and Haugen made a Spot42 consensus secondary structure based on all known "spf" sequences at the time (2015) and found that the spot42 gene is highly conserved across the 5 orders it is identified.

[7] The direct responsiveness of Spot 42 levels to glucose and cAMP is due to repression of spf expression by a cAMP-CRP (cAMP-receptor protein) complex.

The reduction of Spot42 in cells grown in secondary carbon sources is a result of binding of the cAMP-CRP complex to the spf promoter, which negatively regulates transcription of Spot42.

Beisel and Storz demonstrated with microarray analysis and reporter fusions that Spot 42 plays a broader role in metabolism by regulating at least 14 operons.

The identified genes are mostly involved in central and secondary metabolism, as well as uptake and catabolism of non-preferred carbon sources and oxidation of NADH.