As it is well known, messenger RNA has many regulatory regions along its sequence length. One of them is the 5′ untranslated region (5’UTR), which itself contains many regulatory elements such as upstream ORFs (uORFs), internal ribosome entry sites (IRESs), microRNA binding sites, and structural components involved in the regulation of mRNA stability, pre-mRNA splicing, and translation ... [Show full abstract] initiation. Activation of the alternative, more upstream transcription start site leads to an extension of 5′UTR. One of the consequences of 5′UTRs extension may be head-to-head gene overlap. This review describes elements in 5′UTR of protein-coding transcripts and the functional significance of protein-coding genes 5′ overlap with implications for transcription, translation, and disease.