Table I.

Summary of UBC domain-containing proteins, their nomenclature, and activity as ubiquitin E2 enzymes

Previously unnamed UBC domain-containing Arabidopsis proteins were given UBC numbers and grouped together based on sequence similarity (see Fig. 1). InsolubleX, 6×His-tagged protein insoluble when expressed in E. coli; InsolubleY, 6×His-tagged protein insoluble when expressed in either E. coli or insect cells; InsolubleZ, UBC contains predicted transmembrane domain C terminal to UBC domain and protein is insoluble when expressed with predicted transmembrane domain, but soluble when expressed without it. References (as indicated in table by superscript numbers): 1, Sullivan and Vierstra, 1993; 2, Girod et al., 1993; 3, Van Nocker et al., 1996; 4, Bartling et al., 1993; 5, Criqui et al., 2002; 6, Yanagawa et al., 2004; 7, this study; 8, Girod and Vierstra, 1993; and 9, Van Nocker and Vierstra, 1993.

Group No.Gene UBCAGI CodeActive in TEaActive in UbbCommentsGenBank Accession No.
III1At1g14400Yescd,1,7Yes1,8,7E3-ine,7, E3-depf,1,8DQ027016
III2At2g02760Yes7Yes7E3-in7DQ027017
III3At5g62540ndgYes7E3-in7DQ027018
IV4At5g41340Yesh,8,9Yes7E3-in7, E3-dep7DQ027019
IV5At1g63800ndYes7E3-in7DQ027020
IV6At2g46030ndYes7E3-in7DQ027021
V7At5g59300Yesh,3nd
V13At3g46460Yesh,3ndDQ027027
V14At3g55380Yesh,3ndDQ027028
VI8At5g41700Yesh,2,d,7Yes2,7E3-dep7DQ027022
VI9At4g27960Yesd,6ndDQ027023
VI10At5g53300Yes7Yes7E3-dep7DQ027024
VI11At3g08690Yes7Yes7E3-dep7DQ027025
VI12At3g08700ndndInsolubleX7DQ027026
VI28At1g64230Yes7Yes7E3-dep7DQ027041
VI29At2g16740ndYes7E3-dep7DQ027042
VI30At5g56150ndYes7E3-dep7DQ027043
VII15At1g45050Yesi,4Noj,7DQ027029
VII16At1g75440ndNo7DQ027030
VII17At4g36410ndNo7DQ027031
VII18At5g42990ndNo7DQ027032
VIII19At3g20060Yesd,5,7NoDQ027033
VIII20At1g50490ndNoDQ027034
IX21At5g25760ndndInsolubleY7DQ027035
X22At5g05080ndYes7E3-in7DQ027036
XI23At2g16920ndndNot cloned
XI24At2g33770ndndInsolubleY7DQ027037
XI25At3g15355ndndInsolubleY7DQ027038
XI26At1g53020ndNo7DQ027039
XII27At5g50870Yes7No7DQ027040
XIII31At1g36340ndndInsolubleX7DQ027044
XIV32At3g17000Yes7ndInsolubleZ7DQ027045
XIV33At5g50430ndndInsolubleZ7DQ027046
XIV34At1g17280ndYes7E3-dep7, InsolubleZ7DQ027047
XV35At1g78870ndYes7E3-dep7DQ027048
XV36At1g16890Yes7Yes7E3-dep7DQ027049
XVI37At3g24515ndNo7DQ027050
  • a A thioester linkage between the E2 and ubiquitin was observed (examples shown in Fig. 2).

  • b Active in ubiquitination and indicates the E2 showed activity in the transfer of ubiquitin to a peptide linkage (see Fig. 4).

  • c Yes, Activity has been demonstrated.

  • d Ub-UBC conjugate eliminated under sulfhydryl-reducing conditions indicating Ub-E2 thioester linkage, as shown in reference.

  • e E3-in, Ubiquitination of the E2 or other proteins that occurs in the absence of added E3 for E3-independent activity (for an E2 with strong activity, see Fig. 3).

  • f E3-dep, Ubiquitination that requires E3 for E3-dependent (for examples, see Fig. 4).

  • g nd, Protein was not assayed for activity.

  • h Ub, E2 conjugate eliminated under sulfhydryl-reducing conditions, indicating Ub-E2 thioester linkage, but data not shown in reference.

  • i Ub-E2 conjugate not eliminated after incubation under sulfhydryl-reducing conditions, but with 100 mm Lys.

  • j No, No activity was detected.