A heptapeptide repeat contributes to the unusual length of chloroplast ribosomal protein S18 Nucleotide sequence and map position of the rpl33‐rps18 gene cluster in maize

Abstract

The rpl33‐rps18 gene cluster of the maize chloroplast genome has been mapped and sequenced. The derived amino acid sequence of the S18 protein shows a 7‐fold repeat of a hydrophilic heptapeptide domain. S K Q P F R K, in the N‐terminal region. Such a sequence is absent in the E. coli S18 and in the chloroplast S18 of the lower plant liverwort. In tobacco and rice chloroplast S18 it is present 2 and 6 times, respectively. Thus a long N‐terminal repeat (resembling in composition the large C‐terminal heptapeptide repeat in the eukaryotic pol II) appears to be characteristic of monocot cereal S18.

Complete Chloroplast Genome Sequence of a Major Allogamous Forage Species, Perennial Ryegrass (Lolium perenne L.)

“…In both cases, L. perenne showed the shortest of all sequences. Sequence variation between monocots and dicots for rps18 has been described by Weglöhner et al, 33 based on the occurrence of different numbers of the heptapeptide repeat SKQPFRK near the N terminus of the protein. Our study revealed that length differences among Poaceae rps18 sequences are mainly based on the same heptapeptide repeat (S/F)K(Q/K)(P/T)F(R/L/H/S/N)(K/R) as described by Weglöhner et al 33 ( Supplementary Fig.…”

Transmissible familial Creutzfeldt-Jakob disease associated with five, seven, and eight extra octapeptide coding repeats in the PRNP gene.

“…However, there are three other proteins containing consecutive repeats of a heptapeptide or octapeptide whose structure and function may give some insight into variations in the CJD amyloid precursor structure. The maize ribosomal protein S18 has a 7-fold heptapeptide repeat at its N terminus that is thought to have some role in RNA binding (35). The DNA-dependent RNA polymerase II contains many repeats of a heptapeptide in its C-terminal domain, where a regular spacing of proline residues appears to be important in maintaining its unusual secondary structure.…”

Chloroplast ribosomes and protein synthesis.

“…5). The angiosperm S18 proteins have N-terminal extensions compared with E. coli, Marchantia polymorpha, and Cyanophora paradoxa, containing various numbers of repeats of a hydrophilic heptapeptide (686). A C-terminal extension found in the S18 proteins of rice and maize is missing from this protein in tobacco (561,686).…”