Gene and Protein Names in Humans and Mice

Cited from Guidelines for Formatting Gene and Protein Names

In general, symbols for genes are italicized (e.g., IGF1), whereas symbols for proteins are not italicized (e.g., IGF1). 

Although the general rule that gene symbols are italicized and protein symbols are not italicized holds true regardless of the type of organism, there are several variations among organisms in the composition and capitalization of alphanumeric characters within the gene and protein symbols.

Humans, non-human primates, chickens, and domestic species: Gene symbols contain three to six italicized characters that are all in upper-case (e.g., AFP). Gene symbols may be a combination of letters and Arabic numerals (e.g., 1, 2, 3), but should always begin with a letter; they generally do not contain Roman numerals (e.g., I, II, III), Greek letters (e.g., α, β, γ), or punctuation. Protein symbols are identical to their corresponding gene symbols except that they are not italicized (e.g., AFP).

Mice and rats: Gene symbols are italicized, with only the first letter in upper-case (e.g., Gfap). Protein symbols are not italicized, and all letters are in upper-case (e.g., GFAP).

Fish: In contrast to the general rule, full gene names are italicized (e.g., brass). Gene symbols are also italicized, with all letters in lower-case (e.g., brs). Protein symbols are not italicized, and the first letter is upper-case (e.g., Brs).

Flies: Gene names and symbols begin with an upper-case letter if: (1) the gene is named for a protein or (2) the gene was first named for a mutant phenotype that is dominant to the wild-type phenotype (e.g., Rpp30). Gene names and symbols begin with a lower-case letter if the gene was first named for a mutant phenotype that is recessive to the wild-type phenotype (e.g., kis). Gene symbols are italicized. Symbols for proteins that were named for genes begin with an upper-case letter, but there are no accepted formatting guidelines for proteins that were not named for genes. Protein symbols are not italicized.

Worms: Gene symbols are italicized and generally composed of three to four letters, a hyphen, and an Arabic number (e.g., abu-1). Protein symbols are not italicized, and all letters are in upper-case (e.g., ABU-1).

Bacteria: Gene symbols are typically composed of three lower-case, italicized letters that serve as an abbreviation of the process or pathway in which the gene product is involved (e.g., rpo genes encode RNA polymerase). To distinguish among different alleles, the abbreviation is followed by an upper-case letter (e.g., the rpoB gene encodes the β subunit of RNA polymerase). Protein symbols are not italicized, and the first letter is upper-case (e.g., RpoB).