Wu, Q., Wang, X. Z., Tang, Y. Y., Yu, H. T., Cui, F. G., Zhang, J. C. and Wang, C. T. 2014. Molecular cloning, genomic organization and functional analysis of the ribosomal protein L4/L1 (RPL4) gene from Arachis hypogaea. Can. J. Plant Sci. 94: 85-97. The ribosomal proteins have been shown to be important in plant polarity establishment, cell proliferation, leaf shape and auxin-related development. The RPL4 protein is crucial for the maintenance of ribosomal translational efficiency and fidelity. This study concerns the RPL4 gene from Arachis hypogaea. The full-length cDNA (1538 bp) of RPL4 consisted of an open-reading frame of 1221 bp encoding 406 amino acids. The genomic DNA sequence of RPL4 gene consisted of 1491 bp containing two exons and one 270-bp intron. The RPL4 mRNA transcript was mainly expressed in roots and leaves, and fewer signals were detected in stems. The sequence data revealed that RPL4 encoded a typical ribosomal protein L4/L1e domain. Phylogenetic analysis for genes encoding proteins showed that RPL4 were conserved within dicotyledonous and monocotyledonous plants. The ratios of nonsynonymous/synonymous substitution rate (ω=d_N/d_S) were analyzed. No sites were identified under positive selection. In the whole RPL4 sequence, d_S greatly exceeded d_N in all branches of the tree (d_N/d_S<< 1.0), indicating that functional constraints (purifying selection) have acted on RPL4 throughout evolution. The differences among plants and animals and Caenorhabditis elegans may indicate functional differentiation during species evolution.