In an alternative to biosynthesis of nucleotides, most organisms are capable of exploiting exogenous nucleotide sources. In order to do so, the nucleotide precursors must pass the membrane, which requires the presence of transporters. Normally, phosphorylated compounds are not subject to transport, and the utilization of nucleotides is dependent on exogenous phosphatases. The composition of transporters with specificity for purine and pyrimidine nucleosides and nucleobases is subject to variation. The ability of Lactococcus lactis to transport different nucleosides across the cell membrane was characterized at both genetic and physiological level, using mutagenesis and by measuring the growth and uptake of nucleosides in the different mutants supplemented with different nucleosides. Two high affinity transporters were identified: BmpA-NupABC was shown to be an ABC transporter with the ability to actively transport all common nucleosides, whereas UriP was shown to be responsible for the uptake of only uridine and deoxyuridine. Interestingly, the four genes encoding the ABC transporter were found at different positions on the chromosome. The bmpA gene was separated from the nupABC operon by 60 kb. Moreover, bmpA was subject to regulation by purine availability, whereas the nupABC operon was constitutively expressed.

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This paper examines governance responses to Mobility as a Service (MaaS). The analysis focuses on the interactions between public transport systems and MaaS developments in Amsterdam, Birmingham, and Helsinki. Case comparison is informed by the multilevel perspective on sociotechnical transitions and literature on meta-governance of networks. Drawing on these frameworks and empirical findings, the paper identifies six governance approaches to MaaS across cases: analyser, architect, convener, experimenter, lawmaker, and provider. These basic models encompass strategies ranging from hands-on strong intervention to information collection efforts. Consistent with the transitions literature, these six approaches indicate that public transport regimes seek to control the apparent disruptive potential of MaaS by incrementally absorbing innovations; to this end, regime actors adopt governance responses that tend to reproduce existing institutionalised ways of doing and prevailing logics. Furthermore, the six approaches reveal intense interaction between regime and niche, suggesting that a niche-regime space might have emerged in the cases; actors travel and operate across niche, regime, and niche-regimes, mainly driven by concerns with market share and revenue streams in the mobility system.

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