The large subunit of eukaryotic ribosomes contains acidic
phosphoproteins which are related to L7/L12 from Escherichia coli. In the brine shrimp Artemia these
proteins are designated eL12 and eL12'. We have isolated
cDNA clones for these
proteins from a
cDNA bank that was constructed by the use of size-fractionated
poly(A)-rich
RNA (8-10S fraction) from Artemia and a synthetic
oligonucleotide as primer. Clones containing DNA sequences coding for eL12 and eL12 were characterized by hybrid-selected translation and
DNA sequencing. The
proteins eL12 and eL12' share an identical
peptide of 22
amino acids at their carboxy termini whereas the remaining part of the
protein shows little sequence homology. The nucleotide sequences show a different
codon use for the
amino acids in the common carboxy terminus, thereby excluding a common exon coding for this part of both
proteins. Despite the differences in amino acid sequence in the major part of eL12 and eL12' the
proteins have a considerable degree of homology on the basis of the distribution of hydrophobic and hydrophilic
amino acids over the
polypeptide chains, in agreement with a related folding and function of both
proteins. Relative levels of
mRNA coding for eL12, eL12' and
elongation factor 1 alpha were determined during the development of Artemia from a dormant
cyst to a nauplius. The data show a coordinate expression of the genes for
EF-1 alpha and both
ribosomal proteins, excluding a differential expression of the genes for these related
ribosomal proteins during embryogenesis. Analysis of the gene copy number for eL12 and eL12' indicates the presence of a few genes for each
protein.