In the present study, we apply the unitarian theory to explain the pathogenesis of symptomatic VTE: the occurrence of symptomatic VTE is closely related to the compromised immune function as well as the viral infection. This also explains why VTE is frequently found in patients with advanced age, trauma, surgery, malignant tumors, heart failure, immobilization, pregnancy and other risk factors. Our findings provide new knowledge on the etiology and pathophysiology of VTE and novel clue for the clinical diagnosis, treatment and prevention of VTE. Diversity and roles of (t)RNA ligases The discovery of discontiguous tRNA genes triggered studies dissecting the process of tRNA splicing. As a result, we have gained detailed mechanistic knowledge on enzymatic removal of tRNA introns catalyzed by endonuclease and ligase proteins. In addition to the elucidation of tRNA processing, these studies facilitated the discovery of additional functions of RNA ligases such as RNA repair and non-conventional mRNA splicing events. Recently, the identification of a new type of RNA ligases in bacteria, archaea, and humans closed a long-standing gap in the field of tRNA processing. This review summarizes past and recent findings in the field of tRNA splicing with a focus on RNA ligation as it preferentially occurs in archaea and humans. In addition to providing an integrated view of the types and phyletic distribution of RNA ligase proteins known to date, this survey also aims at highlighting known and potential accessory biological functions of RNA ligases. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00018-012-0944-2) contains supplementary material, which is available to authorized users. More recently, split tRNA (Fig. 1A , scheme c) and tri-split archaeal tRNA genes, which encode for parts of the mature domain, have been discovered [17, 18] . This type of tRNA arises from distinct transcription units that are joined by trans-splicing to yield a functional tRNA.